Answer: $7.25
Explanation:
Let T = taco cost
Let M = milk cost
T + M = 2.10
2T + 3M = 5.15
Multiply the first equation by (-2) and add it to the second equation
-2T - 2M = -4.20
2T + 3M = 5.15
M = 0.95
Plug this value for M in to the first equation
T + 0.95 = 2.10
T = 1.15
So a taco costs $1.15 and the milk costs $0.95
1.15 * 3 = 3.45
0.95 * 4 = 3.80
3.45 + 3.80 = 7.25