Excuse me each great god, and I now need to compute a hours, involves [hours: minutes] (for example, 5735:35) between addition, itself is not a big problem, but at the time of calculating all digits, excel will appear error cannot be computed, for example: 12000:6800-40, 15 + itself should answer=18800, 55, but excel cannot be computed, how to solve this problem, please, I need the result can be reached directly 18800:55,

=XX to XX + calculation function, time format is no problem,