怎样用matlab解线性最优化问题,例如minz=8400*x1+7500*x2+6700*x3,约束条件60*x1+65*x2+85*x3<=70,3800*x1+3500*x2+2500*X3>=2900,x1+x2+x3=1,x1,x2,x3>0.