Answer
When all eight cars are running, the intensity level is $107~dB$
Work Step by Step
We can find the intensity of one car:
$\beta = 10~log\frac{I}{I_0}$
$98.0 = 10~log\frac{I}{I_0}$
$9.80 = log\frac{I}{I_0}$
$10^{9.80} = \frac{I}{I_0}$
$I = (10^{9.80})~I_0$
$I = (10^{9.80})~(1.0\times 10^{-12}~W/m^2)$
$I = 6.31\times 10^{-3}~W/m^2$
We can find the total intensity from all eight cars:
$I = 8\times (6.31\times 10^{-3}~W/m^2)$
$I = 5.05\times 10^{-2}~W/m^2$
We can find the intensity level with all eight cars running:
$\beta = 10~log\frac{I}{I_0}$
$\beta = 10~log\frac{5.05\times 10^{-2}~W/m^2}{1.0\times 10^{-12}~W/m^2}$
$\beta = 107~dB$
When all eight cars are running, the intensity level is $107~dB$.
