Let G be a group of order 21, with at least 3 elements of order 3. Prove that G is not commutative, but solvable.

I believe it's got something to do with the 3-Sylow sub-group of G, and there can be either 1 3-Sylow-subgroup or 7 3-Sylow-subgroup. How do I continue this (Surprised)?

Thanks!