For this, all you need is the velocity formula which is Vf = Vi + at.
Vf = final velocity.
Vi = initial velocity.
a = acceleration
t =Â time
Vf = Vi + at.Â
Vf= 0 + (-Â 9.8 m/sec^2) (7s)
*The 0 says that the original velocity is zero. The -Â 9.8 m/sec^2 is gravity because there is nothing else acting upon it, and it is negative because it is falling. The 7s is time time.*
All you have to do then, is simplify to get 68.6 m/s which is B.