The quick method for JK flip flop design (it does not apply to the other types of flip flop) takes advantage of a property of the JK flip flop input equations, where J1 and K1 do not depend on q1, and J2 and K2 do not depend on q2. That is not just a property of this particular problem, but there is always a minimum solution for which this is true (no matter how big the system).