a = length of the top side = 6 cm
b = length of the bottom side = 9 cm
h = height of the trapezoid = 4 cm
The area (A) of a trapezoid can be calculated using the formula:
\[ A = \frac{1}{2} (a + b) \times h \]
Substitute the given values into the formula:
\[ A = \frac{1}{2} (6 + 9) \times 4 \]
\[ A = \frac{1}{2} \times 15 \times 4 \]
\[ A = 7.5 \times 4 \]
\[ A = 30 \]
Therefore, the area of the trapezoid is 30 square centimeters.