Make a proportion.
Do base over height; [tex] \frac{base}{height}[/tex].
[tex] \frac{6}{8} = \frac{21}{h} [/tex]
h is the height of the second triangle. Solve for h.
Cross multiply.
[tex] \frac{6}{8} = \frac{21}{h} [/tex]
6h = 168
h = 28
The height of the second triangle is 28 cm.
