Solve this system of simultaneous equations in order to express V in terms of Vo, x, and a (but not t).
x=Vot+(1/2)at^2
v=Vo+at
solve for t in the second equation.
t= (V-Vo)/a
Put that in the first equation.
x=Vo (V-Vo)/a+ 1/2 (V-Vo)^2/a
multiply by 2a
2ax=2VVo-2Vo^2+V^2-2VVo+Vo^2
2ax=V^2-Vo^2
solve for V^2