There are 200 grams of salt water of A, B, and C respectively, and the concentrations are 42%, 36%, and 30% in turn. Now it is necessary to prepare 420 grams of salt water with a concentration of 34%. How many grams of salt water of type A should be taken at least?
现有甲、乙、丙三种食盐水各200克，浓度依次为42%、36%、30%，现在要配制浓度是34%的食盐水420克，至少要取甲种食盐水多少克？
<result>40</result>