x = cost of 1 taco
2x = cost of 2 tacos
2x+2.50 = cost of those tacos and a salad
1.06(2x+2.50) = increase by 6% for the sales tax
1.06(2x+2.50)+3 = increase by $3 for the tip
1.06(2x+2.50)+3 = 13.60
2.12x+2.65+3 = 13.60
2.12x+5.65 = 13.60
2.12x = 13.60-5.65
2.12x = 7.95
x = 7.95/2.12
x = 3.75
One taco costs $3.75
Unfortunately, none of the answer choices have 3.75. I would ask your teacher for further clarification. It's possible your teacher made a typo somewhere.