Seeing you don't have a graphing calculator, use the web, there are many websites dedicated to different calculators
Answer:
The result is the number of years, approximately, it'll take for your money to double. For example, if an investment scheme promises an 8% annual compounded rate of return, it will take approximately nine years (72 / 8 = 9) to double the invested money
let's multiply both sides by the LCD of all fractions, in this case is 4, just to do away with the denominators for a few seconds