Need help with question 10 asap!!

How much dextrose 70% must be mixed with dextrose 5% to prepare 1,000 ml of dextrose 20%?

1- what do you think the product of a nonzero rational number and an irrational number is? is it rational or irrational? make use of variables, the closure property of integers, and possibly a proof by contradiction to prove your hypothesis.2- why do we have to specify that the rational number must be nonzero when we determine what the product of a nonzero rational number and an irrational number is? if the rational number were 0, would it give us the same result we found in the first question?

Awindow washer cleans 42 windows in 2 hours. at this rate, how many windows did he clean in 180 minutes.