A small loudspeaker radiates sound uniformly in all directions. A microphone placed 2.0 m from the speaker measures a sound intensity I0. When the microphone is moved to 6.0 m from the speaker, the intensity drops to I0/9. The speaker’s vibration amplitude is then increased by a factor of 4 while the microphone remains 6.0 m away. Assuming no other changes, which of the following is closest to the new intensity measured by the microphone, expressed as a multiple of I0?
a) 94I0
b) 916I0
c) 9I0
d) 8116I0