Question

How do i find the base if the hight is 7 and the area is 21

Answer 1

Divide 21 by 7 and you get 3.The base is 3.

Answer 2

If this is about a rectangle, we can use the area equation and solve for the base:
area = height*base
base = area/height
base = 21/7
base = 3

If the figure is a triangle the procedure is the same but the area equation changes a bit:
area = base*height/2