I'm stuck on the following question:

The point P(7cost, 5sint) is on the ellipse with equation [(x^2)/49]+[(y^2)/25]=1. The line through P parallel to the y-axis meets the x-axis at X. The point Q is on the line XP produced so that XQ=2XP. Find, in cartesian form, an equation of the locus of Q, as t varies.

Could someone help please?