You're on the right track. You found that 18% of $12 is $2.16. This is the amount of the tip only. Add this onto original bill $12 to get 12+2.16 = 14.16, which is the final bill (including tip).
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An alternative is to turn 18% into 0.18 and then add 1 to this to get 1.18
When we multiply by 1.18, it will increase the original amount by 18%
So, 1.18*12 = 14.16
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Answer: $14.16
