2.5 years
~You need to set this problem up in the I=PRT form. This should be your formula then, 450=2400(.075)(t). Then do 2400 times .075 and then times that by t which equals 180t. To get rid of that t then take 450 divided by 180 and you get 2.5. Remember when working with rates put them in decimal form also but your time in years.
I hope this helps you:)