An adolescent with meningococcal meningitis is receiving a continuous IV infusion of penicillin G, which is prescribed as 20 million units in a total volume of 2 liters of normal saline every 24 hours. The pharmacy delivers 10 million units/litre of normal saline. How many mL/hour should the nurse program the infusion pump? (Enter numeric value only. If rounding is required, round to the nearest whole number.)