robust optimisation

From : Annonymous

Q: dear all i have a lp model here as follow min = .42*x1 + .56*x2 + .70*x3; s.t. x1 + x2 + x3 = 900; x1 = 400 * y1; x2 = 700 * y2; x3 = 600 * y3; 30*x1 = 12500; 40*x2 = 20000; 50*x3 =15000; ..15*x1 + .2*x2 +.15*x3 = 100; ..2*x1 + .05*x2 + .2*x3 = 100; ..25*x1 + .15*x2+ .05*x3 = 150; y1+y2+y3 = 2; xi=0 yi=0 if x=o yi=1 if x=o the constraints ..15*x1 + .2*x2 +.15*x3 = 100; ..2*x1 + .05*x2 + .2*x3 = 100; ..25*x1 + .15*x2+ .05*x3 = 150; have uncertainties in x1 x2 and x3 coefficients. i want to know how can i make a robust optimisation model for this lp model for example if we know that all the coefficients have variations about 30%. thank you shab .