A worker at a construction site is exposed to a noise of sound intensity equals to 5 x 10-2 W/m2 . After putting on earmuffs, the sound intensity of the noise is reduced to 4 x 10-2 W/m2 . Calculate, in dB, the decrease in sound intensity level after putting on the earmuffs. (Given: Io = 10-12 W/m2 )