Answer:
Part a)

Part b)

Explanation:
Part a)
Level of sound = 75 dB
now we know that

here we know that

now we have


Part b)
Intensity of sound wave is given as

here we know that

so we have


now we know



now we have


In a parallel circuit, the total power supply current is the sum of the
currents through all of the individual branches.
The output current (not the voltage) of the power supply is 5 A.
So the individual currents in the circuit branches is 5 A.
The current through the first 2 resistors is (1 + 0.5) = 1.5 A.
So the current through the 3rd resistor is (5 - 1.5) = <u>3.5 A</u>.