First, we need to calculate the amount of sales tax that was added on to the bill:
Sales tax = 6% of 19.20
Sales tax = 0.06 x 19.20
Sales tax = 1.152
Next, we need to calculate the total amount of the bill including the sales tax:
Total bill = 19.20 + 1.152
Total bill = 20.352
Now we need to calculate the amount of the tip based on the total bill including the sales tax:
Tip = 12% of 20.352
Tip = 0.12 x 20.352
Tip = 2.44224
Rounding to the nearest tenth gives us:
Tip = 2.4
Therefore, John left a tip of $2.4.