To find the population of bunnies after 5 months using the equation \( P = 12(3)^x \), where \( x \) is the number of months since March, we need to substitute \( x = 5 \) into the equation.
\[ P = 12(3)^5 \]
Now we calculate \( 3^5 \):
\[ 3^5 = 3 \times 3 \times 3 \times 3 \times 3 = 243 \]
Now we can plug this back into the equation:
\[ P = 12 \times 243 \]
Calculating \( 12 \times 243 \):
\[ 12 \times 243 = 2916 \]
Therefore, the population of bunnies after 5 months will be 2916.