Guys please answer fast

Which statement about perfect cubes is true

An initial investment of $100 is now valued at $150. the annual interest rate is 5%, compounded continuously. the equation 100e0.05t = 150 represents the situation, where t is the number of years the money has been invested. about how long has the money been invested? use your calculator and round to the nearest whole number. years

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?