Nick has tennis practice every sixth day = 6
Mark has tennis practice every 4th day = 4
They both had tennis practice on = 31st July
We have to find when will be the next time that they both have practice on the same day?
For this, we will find the LCM of 4 and 6
So, LCM of 4 and 6 is 12.
So, it will be 12 days after 31st July, that they will practice on the same day.
So it is 12th August.