First, find how much he paid by tire. To do so, divide what he paid by how many tires he bought like this : 240$ / 12 = 20$ per tire
Then, calculate how much he sells each tire. To do so, start by calculating how much he paid for 3 tires: 20$ x 3 = 60$
This is the price he sells 2 tires for, therefore : 60$ / 2 = 30$ he sells his tires 30$ each.
Finally, you have to calculate the profit he made by selling 12. We already know how much it cost, so you need to find how much money he gets selling them : 12 tires x 30$ = 360$
To find the profit, take off the amount he paid from the amount he made : 360$ - 240$ = 120$