Answer: it will take a fewer minutes less than both the minutes Reuben and Tony will use.
Step-by-step explanation:
If Reuben can do 630 dishes in 105 minutes. Therefore he would wash 630/105 dishes in 1 minute.
And if Tony can do 630 dishes in 70 minutes. Therefore, he would wash 630/70 dishes in 1 minute.
That means that if they wash the dishes together, every minute would mean that they would be able to wash (630/105)+(630/70)=15 dishes in 1 minute.
Since there are 630 dishes to be washed, they would take together
630/15=42 minutes