24= -2(b-3)+8
I suppose you want to solve
24= -2(b-3)+8
for b, am I right?
If so, subtract 8 from both sides to get
16 = -2(b-3)
divide both sides by -2 to get
-8 = b-3
then add 3 to both sides to get
-5 = b
then check the answer
24 = -2(-5-3) + 8 = 16 + 8