This is a pretty large figure, so let us break it into pieces.
-> See attached for how I broke it up and for how I solved
-> The area of a rectangle can be found from doing lengths times width equals area
Things I forgot to clarify in my image:
-> The 4 comes from 10 - 6 = 4
-> The 6 comes from 9 - 3 = 6
Answer:
273.5 mi²