A nurse is preparing to administer vancomycin 500 mg in 250 mL of dextrose 5% in water (D5W) to infuse over 2 hours. The drop factor of the manual IV tubing is 10 gtt/mL. The nurse should adjust 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.)