A progressive wave propagates towards positive-x direction with a velocity of 5 m s-1. The amplitude and wavelength are 15 mm and 40 cm respectively. Calculate the vibrational speed of a particle at position x = 0.5 cm at time t = 0.2 s.

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

Iwas thinking the wavelength is one half its original value