Please do a. and b.

a.   slope =   y1-y2   /   x1-x2  ==== (8-17)/(4-8) = 9/4

     using y = mx+b     m = 9/4    and one of the points

                8 = 9/4(4) + b       b = -1

         y = 9/4 x -1  

b.  slope = 9/4      

       using point   -12 20        20 = 9/4 (-12) + b    b = 47

y = 9/4 x + 47

Picture:

https://www.desmos.com/calculator/vxtm4fbbaa