Answer:
D.
b = 175; which is the initial # of pages to start
Explanation:
you can find the slope to find b or y-intercept (x=0) for equation
y=mx+b
to find m = (y2-y1)/(x2-x1)
(x1,y1) = (9, 100)
(x2, y2) = (15, 50)
m = (50-100) / (15-9) = -50/6 = -25/3
let use point (15, 50)
y=mx+b
50 = -25/3*x + b
50 = (-25/3)*(15) + b
50 = -125 + b
b = 175; which is the initial # of pages to start