Frank,

In all problems like this the idea is to replace something that does not add (hours/container) by something that does (containers/hour).

Obviously if you use more hoses the time goes down not up, so it is clear that hours/container don't add.

It's harder to show rigorously that containers/hour do; the "same size, same pressure, same container" is an attempt, still not rigorous, to justify this. We more or less have to rely on our experience of the physical world to see that making containers per hour additive does make sense.

So: if one hose pipe gives (1/8) container per hour, how many containers per hour do four pipes give? And how many hours per container is this?

Good Hunting!
RD