Thx
image point b'(4, -8) was transformed using the translation (x - 2, y + 3). what were the coordinates of b?

Hello,
The translation t is (x,y)->(x-2,y+3)
So its inverse t^(-1)=-t is (x,y)->(x+2,y-3)

B=-t(B')=(4+2,-8-3)=(6,-11)