You can multiply by 12 because to get rid of the fractions all terms should be divided by the LCM (ie the smallest multiple that is exactly divisible by 2, 4 and 3)
Multiples of 3 = 3, 6, 9, 12
Multiples of 4 = 4, 8, 12, 16
Multiples of 2 = 2, 4, 6, 8, 10, 12
Therefore the fractions should be multiplied by 12
To find the final cost you multiply 35.80 x .07 and you get 2.506 but since its money you round it to $2.51. $2.51 is your sales tax and now you need to add it to the cost of the shirt so 35.80+2.51= $38.31
