Answer:
18
Girl = g
Boy = b
1g 1b 1g 2b 1g 3b
2g 1b 2g 2b 2g 3b
3g 1b 3g 2b 3g 3b
4g 1b 4g 2b 4g 3b
5g 1b 5g 2b 5g 3b
6g 1b 6g 2b 6g 3b
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Another way you can do this,
6 × 3 = 18
In the end there will be 18 selections.