All:

This should be simple but I am clearly missing some of the nuances - can you please help me see what I am doing wrong?  I would like to solve 2 eqns in 2 unknowns:

eq15 := Kzeff15 = (Kvr*Kz15)/(Kvr+Kz15);

eq33 := Kzeff33 = (Kvr*Kz33)/(Kvr+Kz33);

Kz33 := (3.3/1.5)*Kz15;

Kzeff15 := 150612;

Kzeff33 := 253629;

soln_z15 := fsolve ({eq15,eq33},{Kvr,Kz15});