Final answer:
The equivalent resistance of a 60-Ω resistor in parallel with a 20-Ω resistor is computed using the parallel resistance formula, which results in an equivalent resistance of 15 Ω.
Step-by-step explanation:
The equivalent resistance of resistors in parallel is calculated using the formula 1/Req = 1/R1 + 1/R2 + ... + 1/Rn, where Req is the equivalent resistance and R1, R2, ..., Rn are the resistances of the individual resistors.
For the given problem of a 60-Ω resistor in parallel with a 20-Ω resistor, we use the formula: 1/Req = 1/60 Ω + 1/20 Ω. This simplifies to 1/Req = 1/60 + 3/60 = 4/60, therefore, Req = 60/4 = 15 Ω. The closest answer from the options is C. 15 Ω.