If $\frac{4}{3} (r + s + t) = 12$, what is the average of $r$, $s$, and $t$?
The average of $r$, $s$, and $t$, is $\frac{r+s+t}{3}$. Dividing both sides of the given equation by 4, we get $\frac{r+s+t}{3}=\boxed{3}.$