Answer
$v_{f}=\sqrt {v^{2}_{0}+2gh}$ (Same as part a)
Work Step by Step
If a ball is thrown up with a certain speed, it will have the same speed when it returns to the height that it was thrown at. Therefore, the speed of the ball when it hits the ground will be the same if it was thrown up with a velocity of $v_{0}$.
This answer can also be achieved by using the formula from part a: $v_{f}=\sqrt {v^{2}_{0}+2gh}$ Throwing the ball upward instead of downward just means that the initial velocity is negative (if down is positive). Since the initial velocity is squared in the formula, changing the sign of the initial velocity does not change the final velocity.
