A protocol for desalting oligonucleotide solutions specifies centrifugation of a 1,250 uL aliquot of solution at 3300 X g for 30 min. The rotor in your centrifuge has a maximum radius of 4.8 cm. What rpm should you use to centrifuge the solutions? Answer to the nearest whole number.

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