Question 1208652
a)
Since the h is hard to work with when it's inside a square root, we square both sides to get {{{v^2=64h+(v_0)^2}}}. Subtracting {{{(v_0)^2}}} from both sides gives {{{64h=v^2-(v_0)^2}}}. Finally, dividing both sides by 64 gives {{{h=(v^2-(v_0)^2)/64}}}.
b)
Going back to the original formula, we see that we have to plug in {{{h=4}}} and {{{v_0=0}}} from the problem statement. Doing so gives {{{v=sqrt(64*4+0^2)=sqrt(256)=16}}}, so the final velocity is 16 ft/sec.