I'm having difficulty understanding the solution to this question. "A source creates a sound that is observed at 200 Watts per meter squared. If the intensity level of the observed sound decreases by 20 decibels what is the decrease in observed intensity? The way I solved it was I saw 20 decibels as a decrease in intensity of 100 so I subtracted 100 from 200 to get 100 Watts per meter squared but the solution divides 200 by 100 and then subtracts this from the original number: 200 - 2 = 198. Why do they solve it like this and not the way I did?