Creative use of formatting may make this problem clearer to me, to other helpers and perhaps to you as well. As typed, your
31y^3
Sqrt31y^3/9x^6 seems to indicate Sqrt( ----------- )
x^6
31y³
or √( ---------- )
x^6
√31 cannot be reduced.
√(y³) = y√y.
√(x^6) = x³
Putting this all together, we get the final answer
√31*y*√³
( --------------- )
x³