A gun that is spring-loaded shoots an object horizontally. The initial height of the gun is h=5 cm and the object lands 20 cm away. What is the gun's muzzle velocity?

Do i use something like v=sqr(k)/m*x. I am getting something like 3.2m/s, is this somewhat correct at all.

the choices I have are
a. 2.0 m/s
b. 1.0 m/s
c. 3.2 m/s
d. 4.9 m/s
e. 3.9 m/s

d=1/2 g t^2

timeinair= sqrt 2d/g=sqrt.10/9.8=.1sec

horizontal distance=vmuzzle*timeinair
.20/.1=vmuzzle