Lets start with 1A:
The y-intercept is the point where line intercepts the the y axis.
In are equation it is 254 because if you think of it logically then he is starting at 254 and going down until he finishes the book. Now to slope when you are given an equation in slope intercept form it is the number multiplied by x (or coefficient). So in this case it is 40. (Think of it like the rate, 1hr=40pages).
1C:
As I mentioned earlier, the y-intercept represents how many pages are in the book.
1B:
I can't show you an image for graphing but my table might help:
x-coordinate (hours): 1 , 2 ,
y-coordinate (pages):254-40*1=214, 254-40*2=174,
Now draw those 2 points and make a straight line going through them.
They you I got the points is you choose a value for the x coordinate and then plug it in to the equation to get the y-coordinate.
Hope this helps :)