So what you want to do is add 30 + 80 and 40 + 60 until you get the same amount so 30 + 80 = 110 and 40 + 60 = 100 so that is 1 month so now we add again so 30 + 110 is 140 and 100 + 40 =140 so that is 2 months so it would take 2 months for them to have the same amount of money.
