The price of a product is 2100 yuan, and the monthly advertising fee is 4900 yuan. If x products are sold in a month, how much is the profit? Isn't it 2100x-4900, or should we add a bracket to this formula, and because it's a computer answer sheet, it can't be wrong at all? What's the most correct way

The price of a product is 2100 yuan, and the monthly advertising fee is 4900 yuan. If x products are sold in a month, how much is the profit? Isn't it 2100x-4900, or should we add a bracket to this formula, and because it's a computer answer sheet, it can't be wrong at all? What's the most correct way

I don't know the purchase price, so I can't calculate the profit

The school is going to hold an adventure summer camp in the middle and senior grades. There are 360 applicants. The fourth, fifth and sixth grades are allocated according to the ratio of 3:4:5,

There are 120 students in Grade Five: 360 △ 12x4
There are 150 students in Grade 6: 360 △ 12x5
Grade 5 is less than grade 6: 150-120 = 30
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It is known that the adjacent sides of a parallelogram ABCD are equal. If its perimeter is 24, find its sides

The opposite sides of parallelogram are equal,
The adjacent sides of parallelogram ABCD are equal
Then all four sides are equal
Each side = 24 △ 4 = 6

A section of elevated highway has been built in a city, which accounts for 85% of the total length. There are still 4.5 kilometers left to be built. How many kilometers is the length of this elevated highway?
In a city, 85% of the total length of an elevated highway has been built, which is 25.5km. How many kilometers are left?

First question 4.5 / (1-0.85) = 30 km
Second question 25.5 / 0.85 * (1-0.85) = 4.5km