The lateral surface area of a cylinder is just the long side connecting the bases, whereas the total surface area includes both the lateral surface area and area of the two circular bases.

(Imagine a rectangle with the circumfrence of the base as one side and the height as the other being folded around)

(Plus the area of two circles)
The literal difference between surface areas would be the two bases 2πr² if you need that.
Plug in a -20 wherever you see a b
(-20)^2 +4*-20-89/13
400 + -80-89/13
400 - 169/13
400-13
=387
Hope this helps
I'm not sure if interpreted your wording correctly but this is what I got...
w(4)+6=8