I have A and B Coloums
A - coloum shows task completed at what time
B - coloum shows how many task completed

Sheet 1

A B
11:45 1
12:00 2
12:15 4
12:30 0
12:45 1
13:00 1
13:15 1
13:30 2
13:45 4
14:00 0
14:15 2
14:45 1
15:00 1
15:15 1
16:00 1
16:15 1
16:30 2

I need to get the result as shown as in Sheet 2,
Coloum A - Duration in hours
Coloum B - Number of task completed in that duration from Sheet 1

Sheet 2

A B
11:00-12:00 1
12:00-13:00 8
13:00-14:00 7
14:00-15:00 4
15:00-16:00 2
16:00-17:00 3


any help is appreciated