Alex stocks up for winter. He buys 36 cans of vegetable. He pays 80 cents per can for tomatoes and 40 cents per can for corn, for a total cost of $20.80. how many cans of tomatoes does he buy?
16 cans of tomatoes and 20 cans of corn
We are told
Note that  can be simplified (by dividing by 40) to give
Subtracting  from 
(P.S. can you tell me where Alex is buying his canned vegetables? I haven't been able to find any this cheap for decades.)