# Sakurai proof Wigner-Eckart theorem

On page 240 in Sakurai's book "Modern Quantum Mechanics" (Revised edition) you can find a proof of the Wigner-Eckart theorem. I don't understand how you can deduce equation (3.10.36) from equation (3.10.35). I also don't understand why this proportionality factor is independent of m, q and m'. Can someone clarify this?