The equation for the area of a trapezoid is:

$\text{Area}=\frac{1}{2}(\text{base } 1 + \text{base }2)(\text{height})$

Locate the different parts of the equation on the trapezoid.
Then substitute the values and solve the equation to calculate the area.

$\text{Area}=\frac{1}{2}(12+16)(5)$

$\text{Area} = 70\text{ square cm}$

See part (a).