A newer machine can produce 4200 cans in 210 minutes It takes the older machine 280 minutes to produce that many cans If the two machines work together how long would it take them to produce 4200 cans?

Ok, we'll call the machine's N and O.

Machine N produces 4200 cans in 210 minutes, which is 1 can every 3 seconds.

Machine O produces 4200 cans in 280 minutes, which is 1 can every 4 seconds.

Together, they produce 7 cans every 12 seconds, because N produces 4 cans in that time, and O produces the remaining 3 cans.

To get 4200 cans at that rate, it would take 600 rounds of 12 seconds, or 120 minutes (2 hours).