1. The problem statement, all variables and given/known data The soot produced by a garbage incinerator spreads out in a circular pattern. The depth H(r) in millimeters, of the soot deposited each month at distance r kilometers from the incinerator is given by H(r) = 0.115e^(-2r) Write the definite integral for the amount of soot deposited per month in a 5 kilometer radius. 2. Relevant equations 3. The attempt at a solution Looks easy, but something is confusing me. I integrate from 0 to 5 kilometers and multiply H(r) by 2pir, but since these functions give out different units, one in millimeters and one in kilometers, how can I just straight multiply? I divided H(r) by 10e^6 to put the millimeters into kilometers, but the book doesn't do that. The book just multiplies the two functions and integrates from 0 to 5. Why is no unit conversion nessesary?