P(2, 0, -1), Q(4, 1, 0), R(3, -1, 1), S(2, -2, 2)

must find the volume of the parallelepiped with adjacent edges PQ PR and PS.

I tried setting it up and i still didn't come out with the correct answer of 3

...whats confusing me is the amount of points above, there are 4 now, instead of 2, or 3.

please help.