Question

A lighthouse casts a 72-yard shadow at the same time as a 32-foot tall billboard casts a 19-foot shadow.
What is the height of the lighthouse?

Answer 1

This is purely a matter of ratios but it makes the assumption that the light source is from exactly the same point relative to the two objects.
h/(72*3)=32/19
Multiply through by (72*3) to get h