Joaquin buys 3 dozen lightbulbs. After changing the lightbulbs in his house,he has 15 lightbulbs lef

Joaquin buys 3 dozen lightbulbs. After changing the lightbulbs in his house,he has 15 lightbulbs left. How many lightbulbs did he use?

Type 3 dozen into the search engine. We get 36 units.

Now, if Joaquin has 15 lightbulbs left, we subtract 15 from 36: 36 - 15 = 21 lightbulbs used