Risk Free Rate equity, return, provided, one

cyber21

Hi

In one of the CFAI mock exam questions, they provided both the rate of return on 3-month Treasury bills (3.0%) and the rate of return on 10-year Treasury bonds (3.5%), and asked to calculate the cost of equity.

I initially used the 3.0% since I recall RFR is based on T-Bills. But the answer key shows that 3.5% for T-Bonds is used. Is there a reason for this? Thanks a lot.