This figure is four congruent triangles, so we just need to find the area of one, then multiply it by 4.
The area of a triangle is (1/2)bh where b is the base length and h is the height. In this case, b=21 and h=16
A = (1/2)bh
(1/2)·21·16
(1/2)·336
168 ← This is the area of one triangle, so then we multiply it by four:
4 · 168 = 672 in²
