How many inches represent 6 feet

Alex drew a circle with right triangle prq inscribed in it, as shown below: the figure shows a circle with points p, q, and r on it forming an inscribed triangle. side pq is a chord through the center and angle r is a right angle. arc qr measures 80 degrees.

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

Math it's appreciated. (picture provided)