Iam confused on these three questions five, six and seven

With this question! what is process of elimination? ? p. s. my brothers acc got banned so add his new one @ yamauchiyamyam17

The length of a rectangle is x times the square root of 100. the width is one-half y more than three-halves x. given that the area of the rectangle is 125 cm2, which equation could represent the rectangle in terms of x and y? a) 5xy − 15x = 125 b) 5xy + 15x = 125 c) 15x2 − 5xy = 125 d) 15x2 + 5xy = 125

Ineed with number 6 , explain how to get 1978