Since volunteers can be of any sexe (no precision given in your problem), then we can consider the question as how many group of 6 we can make with 12 persons:
It's a combination of 6 chosen among 12
¹²C₆ = (12!)/(6!).(12-6!)
²C₆ = (12!)/(6!).(6!)
¹²C₆ = 924 Ways
