when one to use for required return,when you are given both short-term government bill yield or long-term government bond yield?

Who cares, its the cfa (and authors) who want it that way. They also say blume is 2/3 and 1/3, and that Cobb-douglas is constant return to scale, and taylor rule uses 0.5 weights. I just learn it however they want me to learn it!