(a). The equivalent resistance of a series circuit is the SUM of the individual resistances in the circuit.
(4.75Ω + 15Ω + 21Ω ) = 39.75Ω
(b). Current = (voltage) / (resistance)
Current = (12 v) / (39.75Ω)
Current = 0.302 Amperes (rounded to the nearest MilliAmpere))