Question 798470
You must mean, "rate per drum", when you say, "same rate".  


We want to find the one drum tank-emptying rate.
If 7 drums need 28 minutes, then 1 drum needs {{{7*28}}} minutes, or 196 minutes.


How long in minutes if 8 drums are at work?
{{{8(1/196)}}} tanks per minute, because rates are additive for each drum, and instead of only 1 drum at work, there are 8 of them, the same drums.


The time is 24.5 minutes.