The subcommittee needs to contain 1 out of 3 freshmen, 1 out of 4 sophomores, 1 out of 5 juniors and 1 out of 2 seniors. Assuming order is not important, the number of possibilities to pick the subcommittee members is given by:
The decimal point must be moved 3 places to the right in order to have it behind the first non-zero digit; this gives us the exponent of 3, and since we are moving the decimal to the right, it is a negative exponent.