display end time automatically upon entering start time and time usage

hi

I have a worksheet which contains START TIME in column A, then TIME USAGE in column B and END TIME in column C. User enters start time, followed by the number of time usage in minutes, how could i possibly display the end time automatically in this scenario? how do you add the entered time usage to the start time to display the end time? Say if I enter 1:00 AM at start time and 00:15 minutes on time usage, how can 1:15 AM be displayed on the end time automatically? anyone knows a formula how to do this? I appreciate any response.

Thanks,

Stoey