Time formulas + Conditional formulas for time

Hi there,

My head is stuck, perhaps its due to being my first day at work this week :/

I'm looking to solve this excel mystery which has been haunting me since last week.

I'm trying to find out how:

1. To determine the minutes (potentially hours) between two times eg. Scheduled time of Arrival (STA) 08:00 and Actual time of Arrival (ATA) 08:16 = +
0:16mins

2. Conditional formatting that same (=) cell to colour code <15 is green and >15 is red.

Thank you!!