(a) We know that effective resistance of two resistors connected in series is sum of individual resistances
and for two resistors connected in parallel is given by the expression
Keeping above in mind the effective resistance of the circuit is
Inserting in (1) above and making all in terms of
Assuming that internal resistance of the voltage source is small and is ignored in the calculations
(b) As seen from the circuit, both the Resistor
Text (11.9) [T/I] in the question is not relevant to the circuit.