At a rock concert, a dB meter registered 130dB when placed 2.8m in front of a loudspeaker on the stage. A.) What was the power output of the speaker assuming uniform spherical spreading of sound and neglecting absorption in the air? B.) How far away would the sound level be a somewhat resonable 90dB?
I've solved A part and got the intensity to be 10w/m2.

130db=10log(I/ 10^-12) @ 2.8m
10^13= I/ 10^-12
10=I

I know I'm supposed to be finding r for part b. I know I is proportional to (1/r)^2 but I don't know how to use that to come up with the answer.
Please explain how to do this second part. Thank you.

The decible level of a piano is 60db.
What is the intensity of this sound in w/m 2?