For the parabola x2=4ay(a>0), let P(6a,9a) lie on the curve and let Q be its image after reflection about the axis of the parabola. If S is the focus of the parabola, what is the area of triangle △PSQ (in units of a2)?
(a) 40a2
(b) 60a2
(c) 48a2
(d) 54a2