Geometry

Area =   (12+10) /2  X  10 = 110 cm^2

each cm^2 = 4 mi^2            110cm^2 * 4 mi²/cm2     * 640 acres/mi²  =281600 acres     (edited)

We can convert the 10, 10, and 12 cm's to 2 miles, so that it is

$20, 20, 24$, we can find the area with $(a+b)/2*h$

$(20+24)/2*20=440$

that is 440 square miles, then we multiply by 640

our answer is $440*640$

too lazy to use calculator lol