hiiii i just commented but it works now!
THE ANSWER IS: 9
let the length FJ be x
since the triangles are similar, set up a ratio that matches the corresponding sides
so the longest side of the triangle over the shortest side of the triangle
set the ratios equal to each other
to solve for 16+x, multiply 15x15 then divide by x
rewrite that as 225/x = 16+x
solve for x
you’ll get two answers: -25 and 9
since the side length can’t be negative, the answer is 9
