20/100 = x/12
The 20/100 in the expression represents the 20%. The x in this scenario is the unknown amount in which the person will tip. The /12 is the cost of the original price. So, in order to find the value of x, you would need to cross multiply.
x = $2.40
The total cost would be $2.40 + $12.00 = $14.40
