Proportion can be used to find the height = 0.75
Explanation:
A billboard is 27 feet high and casts a 36-foot shadow at noon.
Height of billboard = 27 feet
Height of shadow of billboard = 36 feet

A fir tree next to the billboard casts a 48-foot shadow.
Height of shadow of fir tree = 48 foot

Proportion can be used to find the height = 0.75