To find the function that represents the total cost \( t \) based on the number of shirts \( m \) that Anna orders, we need to consider both the cost of the shirts and the shipping fee.
The company charges $12 per shirt, which means if Anna orders \( m \) shirts, the cost for the shirts will be \( 12m \). In addition, there is a flat shipping fee of $8.
Therefore, the total cost can be represented by the equation:
\[ t = 12m + 8 \]
So the correct option is:
t = 12m + 8