Answer:
Mary worked 7 and a half hours.
Step-by-step explanation:
The easiest way to solve this is converting to the 24 hours metric.
In this metric, 8:10 am is 8h, 10 min.
3:45 pm is 12+3 = 15h, 45 min.
Rounded to the nearest quarter hour, Mary worked 15-8 = 7h, 45-10 = 35 min, Mary worked 7 and a half hours.
Answer: 0
common denominator is 20
20+4+10 is 34
34/20 is 1 14/20 or 1 7/10