What is the area of the polygon abcde?

The answer is 73.5

To make it a lot easier split the shapes into a rectangle and triangle.
The rectangle is a tad easier because the measurements are given here.

5 x 12 = 60 (rectangle area)

To find the triangle find the base then height. The base is 3cm and the height is 9cm (shown above)

9 x 3 = 27
Divide that by 2 because it's a triangle and you get 13.5.

Add those two numbers and voila you have your answer of 73.5.