What is the principle called the conversation of matter

Anurse is preparing to administer ampicillin 500 mg in 50 ml of dextrose 5% in water (d5w) to infuse over 15 min. the drop factor of the manual iv tubing is 10 gtt/ml. the nurse should set the manual iv infusion to deliver how many gtt/min? (round the answer to the nearest whole number. use a leading zero if it applies. do not use a trailing zero.)