## Elementary Algebra

Let X represent the amount of money that must be invested to raise the earnings to 72 per year. Now, let’s set up a proportion in which one ratio compares the invested amounts and the other ratio compares the corresponding earnings. So, $\frac{500}{X}$ = $\frac{45}{72}$ To solve this equation, we equate the cross products. 500 $\times$ 72 = X $\times$ 45 36000 = 45X Divide both sides by 45. X = 800. 800 dollars must be invested to raise earnings to 72 dollars per year.