I can't get one of the answer options but:
For projectile motion you separate the horizontal and vertical components so that:
Vertical: Horizontal:
S: 3.5 S: 10
U: ? U: ?
V: 0 V: X
a: -9.81 a: 0
t: ? t: ?
The using the SUVAT equations: V squared = U squared + 2as the vertical component of u can be found as 8.29 m per s.
Then the time taken to reach the half way point can be found using V = U + at as 0.85 s.
Then as t for the vertical component is equal to that of t for the horizontal component: S = Ut + 0.5at squared
As a is equal to zero: S= ut, which is 10 = u x 0.85 s. Therefore U is equal to 11.76 m per s.
Then using a squared + be squared = c squared the initial velocity can be found. 11.76 squared + 8.29 squared = 207.02.
The square root of that is 14.4 m per s. But that is not offered on the answer options.