How much additional money must be invested

Question

an investment of $500 earns $45 in a year. At the same rate, how much additional money must be invested to raise the earnings to $72 per year 

Answer 1

500 : 45 :: x : 72          proportion

45x = (500)(72)            product means.extremes

45x = 36,000                simplify

x = 800

 

How much more must be invested?