Question

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

Answer 1

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

Answer 2

The shadow Would be About 6.3 feet