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.
[tex]\bf \stackrel{square}{(320\cdot 207)}~~+~~\stackrel{triangle}{\cfrac{1}{2}(320)(248.24)}\implies 66240+39718.4\implies 150958.4[/tex]
