The basic dimensions of any triangle are its area, base, and height.
They're related by the area equation; the area is half of the base times the height, or:
[tex]A=\frac{1}{2} b h[/tex]
We know the area and the height, so the missing dimension has to be the base. Let's set up an equation by substituting the values the problem gives into the area equation.
[tex]21=\frac{1}{2} \cdot b \cdot 7[/tex]
Can you solve this equation for [tex]b[/tex]?
