The current through each resistor in the two-resistor circuit is the current through the resistor in the one-resistor circuit (the circuit in Part A). The voltage across each resistor in the two-resistor circuit is the voltage across the resistor in the one-resistor circuit.

Serial circuit.   the current is constant.  

            the voltage across a given resistor is half the rating in a one-resistor circuit.

Parallel circuit    the voltage is constant

the current is half the value of the current with a single resistor

Explanation:

To answer exactly this exercise, you need the diagram or the indication of the type of circuit being used, since there are two possibilities, let's consider the results of each one.

Serial circuit.

The two resistance are one after the other.

In this case the current in the resistor sides is the same, that is, the current is constant in the circuit.

The voltage is proportional to the value of each resistor and if the two resistors are equal, the voltage across a given resistor is half the rating in a one-resistor circuit.

Parallel circuit

the two resistance is next to each other.

In this case the voltage is constant, that is, the voltage across the two resistors is the same as in the case of a single resistor.

The current is inversely proportional to the value of the resistance

          i₁ = V / R₁

          i₂ = V / R₂

for a single resistance

           I = V / R

these currents are related

          i = i₁ + i₂

if the two resistors have the same value the current is half the value of the current with a single resistor

v=ir = 3x15 =45 v