Respuesta :
Vince gave 18 dollars because the tip cost $3.00 and the total amount was $18.00.
How you would find the tip is:
Multiply 15 and 20%
20% = 0.2
Then you get 3.
So you add 3 to $15 and you get = $18.00
So the total was $18.00
Hope this helps!!(: