-(k7*x1 + k11*x1 - k1*k2*x4 + k12*x1*x2)/k16 
(k4*x1 - k8*x2 + k5*x1*x3)/k16 
(k6*x1 - k9*x3)/k16 
-(k1*x4 - k3*x3 + k10*x4)/k16 
