If you mix 5 mg GHRP per 2.5 mL of BAC water, your concentration will be 2 mg/mL which equals 2000 mcg/mL.
To get a 100 mcg dose, you'll need 0.05 mL of your solution.
(2000 mcg / 1 mL = 100 mcg / x)
If for your syringe, 40 I.U. equals 1 mL, then you will need to take only 2 units of solution...