Two times louder
Four times louder
Eight times louder
Ten times louder
Correct Answer: Four times louder

A little background…

Instead of increasing linearly, decibels follow a logarithmic scale that raises by powers of ten and every 10dB roughly equates to a doubling in loudness based on the average human hearing. That being the case, 30dB is around twice as loud as 20dB and a computer making 40dB of noise would be about four times louder than one generating 20dB.

A PC producing only 20dB of noise would be considered a pretty quiet system while a typical office is around 40-50dB and comfortable hearing levels are said to be under 60dB. A siren 10 meters away and speakers at a rock concert are around 110dB, heavy weapons and space rockets are 180-190dB and at 194dB sound waves become shock waves.