-43=3(7+b)-7(b+8)

Solution for -43=3(7+b)-7(b+8) equation:

-43=3 (7+b)-7 (b+8)

We simplify the equation to the form, which is simple to understand 
-43=3(7+b)-7(b+8)

Reorder the terms in parentheses
-43=+(+21+3b)-7*(b+8)

Remove unnecessary parentheses
-43=+21+3b-7+*(+b+8+)

Reorder the terms in parentheses
-43=+21+3b+(-7b-56)

Remove unnecessary parentheses
-43=+21+3b-7b-56

We move all terms containing b to the left and all other terms to the right. 
-3b+7b=+21-56+43

We simplify left and right side of the equation. 
+4b=+8

We divide both sides of the equation by 4 to get b. 
b=2