a. As intensity is power per unit area, for a given source `PmuI`. If `L_1` and `L_2` are the initial and final loudness levels, Then we have
`L_2-L_1=10log((I_2)/(I_1))`
The increase in loudness level is
`triangleL=10log((P_2)/(P_1))=10log((400)/(20))`
`impliestriangleL=10[log20]=13dB`
b. Increase in loudness level of sound is
`L_2-L_2=10log((I_2)/(I_1))`
`80-20=10log((I_2)/(I_1))`
`implies6=log((I_2)/(I_1))`
`implies((I_2)/(I_1))=10^6`