we have that
If triangle RST is a right triangle and angle mthen
triangle SUT is a right triangle too
so
In the right triangle SUT
Applying the Pythagorean Theorem
ST^2=h^2+4^2 -------> equation A
In the right triangle RSU
Applying the Pythagorean Theorem
RS^2=h^2+16^2 -----> equation B
In the right triangle RST
Applying the Pythagorean Theorem
20^2=RS^2+ST^2 -------> equation C
substitute equation A and equation B in equation C
20^2=h^2+16^2+h^2+4^2
solve for h^2
400=2h^2+272
2h^2=128
h^2=64
h=8
answer is option 1