A very, very hungry guy goes to a fast food place and orders…

A very, very hungry guy goes to a fast food place and orders 4 burgers and 4 tacos, at a total cost of $12.00. Three days later, he’s ready to eat again. This time, he buys 7 burgers and 2 tacos, at a total cost of $16.50. Find the cost of one burger, and the price of one taco.