We can expand our answer and compare it with the given expression.
3p (2p +1) (2p - 1)
(6p^2 +3p) (2p - 1)
2p(6p^2 +3p) - (6p^2 +3p)
12p^3 + 6p^2 - (6p^2 + 3p)
12p^3 + 6p^2 - 6p^2 -3p
12p^3 -3p
We can see above that after expanding and simplifying, the result is the same as the given expression. Therefore, we can be sure our solution is correct!