first, we'll need the area of a single triangle
then we'll multiply that by 3 to get our answer
to find the are of a triangle, we multiply height times base then divide that by 2
so.. 5 x 10 = 50; 50/2 = 25
if 25 = one triangle
then 25 x 3 = 75 = three triangles
answer - 75 sq. in.
