Final answer:
The appropriate risk-free rate to use when calculating the cost of equity for a firm is a long-term Treasury rate.
Step-by-step explanation:
The appropriate risk-free rate to use when calculating the cost of equity for a firm is A) a long-term Treasury rate. The risk-free rate is used as the baseline for estimating the expected return on equity. Long-term Treasury rates are typically considered the most reliable measure of the risk-free rate because government bonds are considered to have virtually zero default risk.