What is the missing reason for the second step in the proof below (ik the photo sucks)

The last time i bought this product , it cost $20.00 but it looks like it cost 29. 60 today? what is the increase

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

We just started the introduction into circles and i have no idea how to do this.