Help with Maximum Flow Rate?

I already did half the work but I can't figure out the other half!
This is the question:
Begin continuous IV Pitocin at 1.5 milliunit/min. Increase 1.5 milliunit/min every 15 minutes to a maximum of 20 milliunits/min.
Available: 1000mL LR with 20 units Pitocin
What is the flow rate in ml/hr? ANSWER I GOT WAS 4.5 ML/HR
What is the maxiumim flow rate at which the pitocin infusion can be set for the titration as ordered? 

Oct 23, '17The second question can be solved in the same manner in which you determined the beginning infusion rate.

Oct 24, '17Quote from LittleNurseBeeAs chare said, you can solve it in precisely the same manner as your initial flow rate.I already did half the work but I can't figure out the other half!
This is the question:
Begin continuous IV Pitocin at 1.5 milliunit/min. Increase 1.5 milliunit/min every 15 minutes to a maximum of 20 milliunits/min.
Available: 1000mL LR with 20 units Pitocin
What is the flow rate in ml/hr? ANSWER I GOT WAS 4.5 ML/HR
What is the maxiumim flow rate at which the pitocin infusion can be set for the titration as ordered?
You can also recognize that it's a simple proportion problem.
IF 1.5 mu/min > 4.5 mL/hr THEN 20 mu/min > ? mL/hr