For this case, the first thing we must do is define variables.
 We have then:
 x: cost of tacos
 y: cost of enchiladas.
 We write the system of equations:
 2x + 3y = 7.80
 3x + 5y = 12.70
 Solving the system we have:
 x = 0.9 $
 y = 2 $
 Answer:
 each taco and each enchilada was:
 x = 0.9 $
 y = 2 $