How to solve (x + 120) / 56 = x / 50-3? Fast

How to solve (x + 120) / 56 = x / 50-3? Fast

1. Remove the denominator and multiply both sides by 56 * 50
2. Move items and merge similar items
3. The solution is x = 2400

How to solve the equation with 2 / 7, 3 / 5-x = 19 / 35, 1 / 5

2/7+3/5-x=19/35-1/5
=2/7+3/5-19/35-1/5=x
x=2/7+3/5-19/35-1/5
x=2/7+（3/5+1/5）-19/35
x=2/7+（3/5+1/5）-19/35
x=2/7+4/5-19/35
Find out their least common multiple: 35 and then pass it through:
x=10/35+28/35-19/35
x=38/35-19/35
x=19/35
This is the whole process!

There are four numbers, and their average is 34. The average of the first three numbers is 30, and the average of the last two numbers is 36. What is the third number?

(30 × 3 + 36 × 2) - 34 × 4, = (90 + 72) - 136, = 162-136, = 26; a: the third number is 26