How do you simplify 1/ 4( 12- 4t )?

$\frac{1}{4} \left(12 + 4 t\right) = 3 - t$
First, you multiply $12$ by $\frac{1}{4}$. $3$ is $\frac{1}{4}$ of $12$, so it is equal to $3$. Then, multiply $\frac{1}{4}$ by $- 4 t$. $\frac{1}{4}$ of $4$ is $1$, so it is equal to $- 1 t$. $- 1 t$ is equal to $- t$.
Finally, you have your answer, $3 - t$.