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?
The second shirt is 15-6=
<gadget id="calculator">15-6</gadget>
<output>9</output>
9 dollars.
Both shirts cost 15+9=
<gadget id="calculator">15+9</gadget>
<output>24</output>
24 dollars.

<result>24</result>