Answer:
3:30 (Three hours and thirty minutes)
Every hour has 60 min, so:
From 9:15am to 10:00am he worked 45min;
From 10:00am to 12:00am he worked 2h;
From 12:00am to 12:45pm he worked 45min;
Now we sum everything:
45 + 45 = 90min = 1:30h
1:30 + 2h = 3:30
Hope it helped,
BioTeacher101
