Exercise $4$

Your favorite uncle has just left you $$20,000.$ You are not a big drinker and enjoy watching video on Saturday night so there is no temptation to spend the money. You decide to invest the lump sum in a bank earning interest at a rate of $0\mathrm{.}5\%$ per month. You see a house that you want to buy since you dislike your current flatmates $($they party a lot and disturb your studies$).$ Unfortunately, the deposit for the house is $$30,000.$ If you can save $$100$ a month from your student loan, how long will it take to accumulate the $$30,000?$