Decide if this is a permutation or combination

When only separate discreet points are graphed it is called?

How do you use the elimination method for this question? explain, because i really want to understand!

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