20. Oil is pumped out from a tank at the rate of
\( \frac{20e^{-0.1t}}{1 + e^{-t}} \) gallons per minute, where \( t \) is measured in minutes.
To the nearest gallon, how many gallons of oil are pumped out from the tank during the time interval
\( 0 \leq t \leq 6 \)?
