John buys 2 shirts. The first shirt costs $6 more than the second shirt. If the first shirt costs $15, how much, in dollars, did the shirts cost in total?
Please answer the following question by reasoning step-by-step.
24
The second shirt is 15 - 6 = 9 dollars.

Both shirts cost 15 + 9 = 24 dollars.

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The answer: 24