Please help. I am a LPN and bridging to my RN. I missed 1 question on my drug calculations competency test today and so I have to retest next week which my instructor informed us would be harder. I am a nervous wreck. Some of the questions she advised us to look over have to do with time. I am not sure what formula to use for these problems. One she had on a worksheet but didn't work out for us was this: A patient is to be given 1000 ml by IVI using a controller with a drip factor of 15 drops/ml. The infusion starts at 8.00am and every four hours the patient is given a 1hr rest. If the drip rate was set at 25 drops per minute, how much liquid would be left at 3.00pm?