I have the 5th edition. Cm and Ct are discussed in Chapter 14-11 and Chapter 14-15 respectively. Admittedly, it took a LONG while to find it, and since the exact equation given in the problem is not included in this edition, I'm not 100% certain this is what they are referring to, but it seems to be appropriate from my understanding of the problem.
Cm is the load distribution factor relating to spur and helical gear loads on a shaft. If you assume accurate mounting, the ranges given in the table are from 1.3 to 1.8
Ct is a temperature factor and for oil or gear -blank temperatures up to 250Deg. F use Ct =1.0.
If you have a different edition, you might try searching under "Application Factors" in the appendix.
