Exponential and Logarithmic Functions · Superchallenge problem

Sound level in decibels is $L=10\log_{10}\dfrac{I}{I_0}$, where $I$ is the intensity and $I_0$ a fixed reference intensity. One loudspeaker produces a sound level of $80$ dB at a certain spot, and when several identical loudspeakers play together their intensities add. What is the least number of these loudspeakers needed to produce a sound level of at least $95$ dB at that spot?