I'm trying to set up a system of three equations. I have two of them, but I can't get the third. Anyone know what to do? Here's the problem:
Jane's employer gave her a bonus of $1600. She decided to invest all the money, some at 5%, some at 7%, and some at 8%. She invested three times more money at 8% than she did at 5%. At the end of one year the total interest she earned was $115.
Here are the first two equations of the system I've found:
x + y + z = 1600 .05 x + .07y + .08z = 115
I'm stumped as to what the third one is. I need the third one to solve and figure out how much money this bitch invested in each. Can anyone help? Thanks in advance.