Maximize[0.12 x1+0.06 x2+0.08 x3,{x1+x2+x3<=100000,x2+x3>=0.4 (x1+x2+x3),x1<=0.5 (x1+x2+x3),x1>=0,x2>=0,x3>=0},{x1,x2,x3}]