Hirn would like to estimate the area of nevada using a trapezoid. he uses the dimensions shown as approximation. what is the approximate area of nevada.

check the picture below.

so the area Hien outlined is just a 207x320 rectangle and a triangle with a base of 320 and a base of "h", now using the pythagorean theorem, we can see that h ≈ 248.24, now recall that the area of a triangle is A = (1/2)bh.

so let's get the area of those two, sum them up and that's the area Hien outlined.