Question

the velocity acquired by a body moving with uniform acceleration is 12 m/s in 2 sec and 18 m/s in 4 sec . Find initial velocity of the body

Answer 1

18-12=6
6/2 =3m/s^2
v=u+at
v=12+(3)(-2)
v=6
initial speed = 6m/s

Answer 2

Using the equation:
$v=u+at$
we get, 
$u+2a=12 \\ u+4a=18$
On solving these equations we get, 
$u=+6 m/s \\ a=+3 m/s^2$