In general the area of a rectangle is given by:

Where a and b are the length of the sides.
From the picture of above we see that the figure can be divided in two rectanbles, 1 and 2.
1) The area of the first rectangle is:

2) The area of the second rectangle is:

The total area of the figure is just the sum of the areas of the rectangles which form it:

Answer
The area of the figure is 45 ft²