Curve C has equation y= (1/3)x^3 - 4x^2 + 8x + 3

The point P has coordinates (3,0) and lies on C. Point Q also lies on C. The tangent to C at Q is parallel to the tangent to C at P.

Find the coordinates of Q-

I found the tangent to C at P- y = -7x +21

And that the gradient of the tangent on C at Q will be -7 but I can't think how to get the coordinates.