When the speaker S_1 is switched O N , the sound intensity at a...

When the speaker $S_1$ is switched $O N$, the sound intensity at a point $P$ in a room is 80 dB . But when the speaker $S_2$ is switched ON ( $S_1$ is switched OFF), the sound intensity at the same point $P$ in the room is 85 dB . The sound intensity level (in dB ) at the same point P in the room, if the two speakers $S_1$ and $S_2$ are simultaneously switched $O N$, is (consider the speakers to be incoherent)