Looks like you have most of the details already, but you're missing one crucial piece.
is parameterized by

for
and
, and a normal vector to this surface is

with norm

So the integral of
is

1) Type of motion: constant acceleration.
2) acceleration, a = 9.8 m/s^2
3) time up = time down = 4seconds / 2 = 2 seconds
4) formula = Vf = Vo - a*t^2/2
Vf = 0 => Vo = a*t^2 / 2 = 9.8m/s^2 * (2 s)^2 / 2 = 19.6 m/s
Answer: 19.6 m/s
Y-intercept: 3
x-intercept: 2
put (0,3) and (2,0) as points on the graph