Answer:
v = 12 km/h
Explanation:
To find how much she should increase the speed first we need to find the distance traveled:
 
 
Where:
d: is the distance traveled =? 
v: is the velocity = 8 km/h
t: is the time = 15 min (9:00 to 9:15)
 
 
Now, we can find the speed:

Therefore, she should increase the speed to 12 km/h to reach the office at 9:10 am. 
I hope it helps you!