A client is brought to the emergency center for fluid replacement after running a marathon, and the healthcare provider prescribes a 500 mL bolus of 0.9% normal saline to be administered over 4 hours. The infusion set delivers 10 gtt/mL, so the nurse should regulate the infusion to deliver how many gtt/minute? (Enter numerical value only. If rounding is required, round to the nearest whole number.)