[填空题]
At a rock concert, a dB meter registered 1 dt:e2 a5hvn+)nney 4isi8fo/p ll w:*30 dB when placed 2.8 98dwu 9y2kwq zobc0v+m in front of a loud9uck 9o 2zb ww0q+y8dvspeaker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$ $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB? $ \times10^{2}$m
