Answer:
45 km^2 (C)
Explanation:
Isolate the smaller square -
We only need two side lengths, take 3km and 3km.
3×3 = 9km^2, that's the area of the smaller square.
Isolate the larger square -
Take 6km and the other 6km
6×6 = 36km^2
Add the square's areas together to get the whole area -
36 + 9 = 45km^2
All you need to do to solve these problems is to isolate the shapes and find their area's, and finally add them together.