Solve the triangle using similarity

15. The left triangle is similar to the whole triangle. The x of the small triangle is proportional to the hypotenuse of the large triangle (9+16 =25). the x of the large triangle is proportional to the 9 unit leg of the small triangle.  this creates the proportion . Cross multiply to get  take the square roots of both sides to get x=225

B? ? i'm most likely wrong but i think it would be b