Two cheaper books = x
more expensive = 1.5x
so, 2.5x=150
150/2.5=x=60
therefore the more expensive book = 90
The formula for slope is 
In this case:

so...


-1 <<<The slope
Hope this helped!
~Just a girl in love with Shawn Mendes
Answer:
The slope is 0.
Step-by-step explanation: