Equation C. :) lalalalalala
The slope is the change in Y over the change in X
The change in y is -2-0 = -2
The change in X is 3-9 = -6
The slope is -2/-6, which simplifies to 1/3
The answer to your question is D.
Required expression is x/9 - 7
Two cheaper books = x
more expensive = 1.5x
so, 2.5x=150
150/2.5=x=60
therefore the more expensive book = 90