10(the number of tests) divided by 5(the amount of weeks)=2. That is 2 tests every week. 2x7 weeks is 14 tests.
Or this could be a trick question and he could have only had tests for 5 weeks.
10.75*2.45= $26.3375 + $.06 + $4.97 + 0.026 = $31.3935 - $20 = $11.3935
≈ $ 11.40
Food tax applies on to gum of 0.65 = 0.026
You isolate the variable (a)
-3a = -18
/-3
a = 6