a) To subtract 2 hours 45 minutes from 4 hours, we need to convert the minutes to hours.

2 hours 45 minutes = 2.75 hours

So, 4 hours - 2.75 hours = 1.25 hours

Therefore, a) 4 hours - 2 hours 45 minutes = 1 hour 15 minutes.

b) To find the duration from 4:55 pm to 5:35 pm, we subtract the start time from the end time.

5:35 pm - 4:55 pm = 40 minutes

Therefore, b) 4:55 pm to 5:35 pm is 40 minutes.