3(b+7)=-6b+3(3+b)

Solution for 3(b+7)=-6b+3(3+b) equation:

3(b+7)=-6b+3(3+b)

We simplify the equation to the form, which is simple to understand 
3(b+7)=-6b+3(3+b)

Reorder the terms in parentheses
+(+3b+21)=-6b+3*(3+b)

Remove unnecessary parentheses
+3b+21=-6b+3+*(+3+b+)

Reorder the terms in parentheses
+3b+21=-6b+(+9+3b)

Remove unnecessary parentheses
+3b+21=-6b+9+3b

We move all terms containing b to the left and all other terms to the right. 
+3b+6b-3b=+9-21

We simplify left and right side of the equation. 
+6b=-12

We divide both sides of the equation by 6 to get b. 
b=-2