Your figure is good.
You don't need trig.
You have a right triangle with two known sides, so just use the Pythagorean theorem to find the third side.
The sides measuring 325 m and 500 m form the right angle, so they are the legs.
The side you are looking for, x, is the hypotenuse.
leg1^2 + leg2^2 = hyp^2
325^2 + 500^2 = x^2
105,625 + 250,000 = x^2
x^2 = 355,625
x = sqrt(355,625)
x = 596.343
Answer: 596 ft
