#### Answer

$n=5$

#### Work Step by Step

We need to get the n alone. Thus, we cancel out the subtraction by adding 4 on both sides. This leaves us with the equation $3n=15$. In order to cancel out multiplication, we use division, so we divide both sides by 3 to get that $n=5$. We plug 5 in for n and confirm that our answer is, indeed, correct.