If a 40 -foot tree casts a 12 -foot shadow, find the length of the shadow cast by a 21-foot tree.

Ratio and proportaion

assuming the shadow to the actual height is constant

shadow:actual height=12ft:40ft=12/40=3/10=3ft:10ft

so

3ft:10ft=?:21ft

solve

3ft/10ft=?/21ft

times both sides by 21ft

63ft/10=?

6.3ft=?

the shadow is 6.3ft

The shadow Would be About 6.3 feet