Man whatever muscle you put 4 CC's into won't be happy
I'm guessing the test is 250mg/mL and the deca is 200mg/mL so you are aiming for 500 test and 400 deca which is perfect. You'll want to break them up into something like Monday/Thursday. You can do 2cc each time.
Follow this:
alcohol swab on the top of the deca vial
drawing needle on 5mL syringe: Suck your test out of the amp. Hold upright and pull the plunger down until you pull in a mL of air. Stick that in the deca vial, push the air out, and draw in a mL of deca. Hold upright again and draw in some air to clear the needle. Switch to pinning needle, get rid of the air and inject 2mL of combined test/deca