Hi VJesus12,
We're asked for the total possible number of combinations of four-person foursquare teams that could be chosen from a group of six kids. I agree with Brent's assessment (it's not perfectly clear whether we're supposed to be treating this question as a Permutation or a Combination). That having been said, the 'intent' of this question is that it's meant to be a Combination Formula question:
N!/(K!)(N-K)! where N is the total number of people and K is the size of the 'subgroup'
With 6 children and a group of 4, we have.... 6!/(4!)(2!) = (6)(5)/(2)(1) = 15 possible groups of 4.
Final Answer: B
GMAT assassins aren't born, they're made,
Rich