Minimize[3 x1+4 x2+5 x3+6 x4+7 x5+8 x6,{x1+x2+x3+x4+x5+x6==100,0.15 x1+0.25 x2+0.30 x3+0.10 x4+0.35 x5+0.20 x6>=20,0.35 x1+0.20 x2+0.25 x3+0.50 x4+0.10 x5+0.15 x6<=25,0.20 x1+0.10 x2+0.30 x3+0.15 x4+0.40 x5+0.25 x6<=30,x5<=15,x6<=10,x1>=0,x2>=0,x3>=0,x4>=0,x5>=0,x6>=0},{x1,x2,x3,x4,x5,x6}]