Avillage maintains a large tank with open top with water. the water can drain out of the tank through a hose of diameter 6.60 cm. the hose ends with a nozzle of diameter 2.20 cm. a rubber stopper is inserted in the nozzle. the water level in the tank is kept 7.50 m above the nozzle. (a) calculate the frictional force exerted by the nozzle on the stopper. (b) the stopper is removed. what mass of water flows from the nozzle in 2 hr?

The answer would be a) -80of

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current