We can solve this problem by simply using ratio and proportion. Let us call the height of the flagpole to be X. Therefore the ratio and proportion would be:
3 ft is to 4 ft and X ft is to 72 ft
3 / 4 = X / 72
X = (3 / 4) * 72
X = 54 ft
The height of the flagpole is 54 ft.