Help with an investment matrix word problem!! Can anyone give me the 3 equations in general form that I need to solve this matrix? A person will put 30% of his investment into a stock fund that earns a 9% annual rate of return. He will put 20% in precious metals currently growing at 40% and the remainder into bond funds earning 3%. His goal is to have $4000 of interest income. How much should he put into each investment? One of the equations should be the equation for the statement about interest.