1. A certain automobile transportation company transports a batch of goods. If each vehicle transports 3 tons more, 50 vehicles can transport it completely. If each vehicle transports 1 ton less, 60 vehicles can transport it completely. Under normal circumstances, how many tons of goods can each vehicle transport? 2. Two trains are running in the same direction on parallel tracks, and the front of car a is at the rear of car B. car a travels 1100 meters per minute and car B 800 meters per minute. The body of car a is 120 meters shorter than that of car B. It takes two minutes for car a to catch up with car B and completely surpass car B? 3. In order to beautify the class environment, the class life committee member went to sell the flowers of Grade A, B and C for 39 yuan. The flowers of Grade A, B and C were 4 yuan, 5 yuan and 6 yuan respectively. The life members bought 8 pots of flowers and just ran out of money. How many pots did they sell? 4. If we add natural numbers a and B to the numerator and denominator of the fraction 28 / 43, the result is 7 / 12, then what is a + B equal to?

1. A certain automobile transportation company transports a batch of goods. If each vehicle transports 3 tons more, 50 vehicles can transport it completely. If each vehicle transports 1 ton less, 60 vehicles can transport it completely. Under normal circumstances, how many tons of goods can each vehicle transport? 2. Two trains are running in the same direction on parallel tracks, and the front of car a is at the rear of car B. car a travels 1100 meters per minute and car B 800 meters per minute. The body of car a is 120 meters shorter than that of car B. It takes two minutes for car a to catch up with car B and completely surpass car B? 3. In order to beautify the class environment, the class life committee member went to sell the flowers of Grade A, B and C for 39 yuan. The flowers of Grade A, B and C were 4 yuan, 5 yuan and 6 yuan respectively. The life members bought 8 pots of flowers and just ran out of money. How many pots did they sell? 4. If we add natural numbers a and B to the numerator and denominator of the fraction 28 / 43, the result is 7 / 12, then what is a + B equal to?

Let x tons be transported in normal time. According to the meaning of the question, because the total amount of goods is equal, so (x + 3) * 50 = (x-1) * 60, the solution is x = 21
Answer to the second question: car a is 240 meters, car B is 360 meters. Solution: if the length of car a is x, then the length of car B is x + 120. According to the question, if car a catches up with and exceeds car B, it's necessary to walk more. The length of car B plus the length of car a, that is, x + 120 + X, while car a is 300 meters faster than car B every minute, and it takes 2 minutes to catch up with and exceed car B, so x + 120 + x = 2 * 300, the solution is x = 240
Answer to the third question: A is 2, B is 5, C is 1, or a is 3, B is 3, C is 2, or a is 4, B is 1, C is 3 solution: let a be x, B is y, then C is 8-x-y (XY is all integers). According to the meaning 4x + 5Y + 6 (8-x-y) = 39, we get 2x + y = 9, and because XY is all integers, and the sum of XY cannot be greater than 8, we get x = 2, y = 5 or x = 3, y = 3 or x = 4, y = 1
Answer to the fourth question: 19x + 5 (x is a natural number, that is, x = 0,1,2,3,...) Solution: from the meaning of the question, 28 is a multiple of 7, then a must be a multiple of 7, let a = 7x, then B = 12x + 5, the final sum to a + B is shown in the answer