Answer:
The formula of a trapezoid is:
B1(base 1) + B2(base 2) x H(height) x 1/2 (basically just dividing by 2)
In this case 9 and 3 are your bases so add them together to get 12.
Now we multiply 12 to the height! 12 x 3(height) = 36. Now we multiply 36 to 1/2 which is just dividing by 2, so 36 divided by 2 = 18
