#### Answer

$n=9$

#### Work Step by Step

We start with the given equation: $3(n-4)=15$
We apply the distributive property to simplify the left side of the equation: $3n-12=15$
We add $12$ to both sides of the equation: $$3n-12+12=15+12$$$$3n=27$$
We divide by $3$ on each side of the equation: $$\frac{3n}{3}=\frac{27}{3}$$$$n=9$$