The area \( A \) of a trapezoid can be calculated using the formula:
\[ A = \frac{1}{2} \times (b_1 + b_2) \times h \]
where \( b_1 \) and \( b_2 \) are the lengths of the two bases, and \( h \) is the height.
In this case:
- \( b_1 = 9 \) feet
- \( b_2 = 15 \) feet
- \( h = 12 \) feet
Substituting the values into the formula:
\[ A = \frac{1}{2} \times (9 + 15) \times 12 \]
Calculating \( 9 + 15 \):
\[ 9 + 15 = 24 \]
Now substitute back into the formula:
\[ A = \frac{1}{2} \times 24 \times 12 \]
Calculating the multiplication:
\[ A = 12 \times 12 = 144 \]
Thus, the area of the trapezoid is
\[ \boxed{144} \text{ square feet.} \]