IV MATH HELP: unit/hr

Hello.
For the most part I understand IV math (gtt/min, ml/he etc), but I am having a hard time with unit type questions. I have looked throughout medspub and several websites that I normally use. All the help I have found up to this point is that 1mL = 100 units, but I still cant figure out how to solve these type of problems.

Ordered: Heparin 25,000u/500mL to run at 1200u/hr
How many ml/hr will I start pump at?
**** I don't understand how the answer 24mL/hr. Is there a formula for these problems, I am sorry but I am so confused.

Any help is very appreciated.
Thank you.
Missy

So I understand that part now and have pracitced it on my homework but after looking futher ahead there are other problems that i am getting hung up on. They are the same concept but different....

A client is to receive Heparin 25,000 u in 500mL of D5W at 7mL/hr. How many units per hour will the pt receive?

*** So my papers say the answers 350u/hr, but I dont know how to going about the set up when it says 7mL/hr?

ANY HELP PLEASE, THANKS!!!!

Thank you... I was confusing myself trying to set it up!!!!! MUCH HELP!