The power output of a tuba is 0.39 W.

Question

At what distance is the sound intensity of
the tuba 1.4 × 10−3 W/m2?
Answer in units of m

Answer 1

Really not a good question, as a tube is NOT an isotropic sound source. Ignoring that bit of reality, assumeing it is an isotropic source, then

.49=1.4E-3*4PI*distance^2