For the first part, we are looking for Vf when dy=11.0
Upward is positive, downward is negative.
So Vf = square root [2(-9.8)(11.0) + (18.0)^2]
Vf = 10.4 m/s your answer is correct.
For the part b, t is equals to the time took to reach and dy is equals to 11.0
you did, 11= 18t m/s-(1/2) 9.8t^2 then -11 + 18t- 9.8t^2. By quadratic formula, for the way down the answer is 2.9 s while on it's way up, the answer is 0.77 s