1. The distance of the centre of the circle to the x-axis (y = 0) has to equal the radius. (Why?) Therefore ......

2. (a) By symmetry, p = 0 (draw a rough sketch to see why). Then x^2 + (y - q)^2 = 25^2. Now sub either of (-7, 0) or (7, 0) and solve for q.

(b) (0, q + 25) and (0, q - 25) (why?)