Answer
$P = 270~W$
Work Step by Step
We can calculate the intensity of the sound wave as:
$\beta = 10~log(\frac{I}{I_0})$
$log(\frac{I}{I_0})= \frac{\beta}{10}$
$10^{log(\frac{I}{I_0})}= 10^{\frac{\beta}{10}}$
$I= I_0~10^{\frac{\beta}{10}}$
$I= (10^{-12}~W/m^2)~10^{\frac{115}{10}}$
$I = 0.316~W/m^2$
We then find the power output of the speaker as:
$P = I~A$
$P = I~(4\pi~R^2)$
$P = (0.316~W/m^2)(4\pi)(8.25~m)^2$
$P = 270~W$
