For this problem, let x be the width and y be the length of the rectangle. We use these variable to make an equation from the perimeter.
Perimeter = 2*Length + 2*WIdth
Perimeter = 2y + 2x
70 = 2y + 2x
The area of a rectangle is equal to the product of x and y. Since we want the equation in terms of x only, let's find y in terms of x.
y = 35 - x
Hence, the formula for area is:
Area = xy
Area = x(35 -x)
Area = 35x - x²