Alvin owns coconut trees that yield 5 coconuts each. If a coconut can be sold for $3 and Alvin needs $90, how many coconut trees does he have to harvest? Let's think first. Chain of thought:
Alvin needs to harvest 90 / 3 = 30 coconuts to earn $90. Therefore, the total number of trees that he has to harvest is 30 / 5 = 6.
Therefore, the answer is 6.