Carlos is training for the Olympics. His first training session lasted for one hour and he increases each training session by ten minutes every time. After fiteen sessions, how many minutes will be spend training?

one hour + 15*1/6 hour.

Now multiply by sixty to get minutes.

If you want the total number of minutes set it up as an arithmetic series,
the first term is 60
the common difference is 10 and the number of terms is 15

Use the sum of terms formula, then break the total minutes back down to hours and minutes.