9=-3(5n+4)-4(3+n)

Solution for 9=-3(5n+4)-4(3+n) equation:

9=-3 (5n+4)-4 (3+n)

We simplify the equation to the form, which is simple to understand 
9=-3(5n+4)-4(3+n)

Reorder the terms in parentheses
9=+(-15n-12)-4*(3+n)

Remove unnecessary parentheses
+9=-15n-12-4+*(+3+n+)

Reorder the terms in parentheses
9=-15n-12+(-12-4n)

Remove unnecessary parentheses
+9=-15n-12-12-4n

We move all terms containing n to the left and all other terms to the right. 
+15n+4n=-12-12-9

We simplify left and right side of the equation. 
+19n=-33

We divide both sides of the equation by 19 to get n. 
n=-1.7368421052632