18 is the 20% of what number

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.

Can someone me do math because i am having a breakdown rn because i don’t get it

Write the rational number in lowest terms 99/-15