<human>:  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?
<bot>: How much does the second shirt cost? ** The second shirt is 15-6=<<15-6=9>>9 dollars.
How much did the shirts cost in total? ** Both shirts cost 15+9=<<15+9=24>>24 dollars.
#### 24