Gil buys 4 books for $16. Then he sells 3 CDs for $27. Write equations for y, Gil's change in money after buying a book, and for x, his change in money after selling a CD, in
standard form. What is the slope of each equation?

A. 4y=-16; Slope = 0
3x= 27; Slope = undefined

B. -4y=16; Slope = undefined
-3x= 27; Slope = 0

C. 16y= 4; Slope = -1/4
27x= 3; Slope = 1/9

D. 16y=-4; Slope: -4
27x= 3; Slope: 9
Can anyone explain how they got the equations step by step? THANKS!!