Answer
$12+9t$
Work Step by Step
Original expression: $8+(9t+4)$
Combine like terms. 8 and 4 are the only terms we can combine because there are no other $t\\$s in the expression.
$8+4=12$
We are allowed to add these numbers because of the associative property of addition.
The expression should now look like this: $9t+12$
It is impossible to simplify this further because all like terms have already been combined. So your final, simplified answer is $9t+12$.