Your answer is 40mm
3+12+12+13
=40
2nd subtraction property.
The area of a triangle in determined by the formula:

where b is the base of the triangle and h is it's height
You just have to replace the b and h with their values in the formula (b=9.9ft and h=5.5ft)
The answer is 27.225 ft^2
Angles c and e are vertical