Final answer:
Justin paid a total of $13.80 for his lunch and a 15% tip, after calculating the tip amount of $1.80 and adding it to the original lunch cost.
Step-by-step explanation:
To calculate how much Justin paid for his lunch including a 15% tip, first determine the amount of the tip by converting the percentage to a decimal and then multiplying by the cost of the meal. To convert the percentage to a decimal, divide by 100: 15% becomes 0.15. Then multiply this decimal by the cost of the lunch.
The calculation will look like this:
0.15 × $12.00 = $1.80
The tip amount is $1.80. Add this to the original cost of the lunch to find the total Justin paid:
$12.00 + $1.80 = $13.80
So, Justin paid a total of $13.80 for his lunch and the tip.