Hi. Unfortunately there is no statement to determine if it's true or not. However, I would just give the correct statement.
Secant function is the inverse of cosine. In trigonometry, a right triangle has one 90 degrees angle. It consists of the hypotenuse(h), the adjacent side (a), and the opposite side(o), with respect to the angle. For cosine, it is adjacent over hypotenuse. Since secant is the inverse, it would be hypotenuse/adjacent. Hypotenuse is the longest side.
Hence, sec theta = 15/9
I hope this helps :)