The answer to the ninth question on page 64 of the second volume of a set of mathematics books for five years.
Prepare 18kg antiseptic liquid containing 50% antiperspirant with two kinds of liquid medicines containing 30% and 75% respectively, and how much each liquid medicine should be taken (solved by binary linear equation): suppose xkg containing 30% medicine and ykg containing 75% medicine, according to the meaning of the question: x+y =1830.