An electron moving with initial velocity v0 = 8.6x105 m / s penetrates a region where the electric field equals e = 4.1x10^3 n / c. calculate: a) the time it takes for the electron to reach rest; b) the distance traveled by it before stopping.

The answer is  a.first and third quarters 

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