What Equation was used for solving this problem? (problem already solved)?

One a distant planet, the acceleration due to the gravity is just 2m/s^2. How fast is a dropped rock after 5s? The answer is 10 m/s. But which equation was used to solve this? Is it D=1/2(g)t^2 and/or d=vt. Show how this was solved. (Thank you)