From the equation you can tell that your particle is moving with a costant acceleration. The generic movement equation is [tex]x= x_0 +v_0 t + \frac 1 2 a t^2[/tex] , and velocity is given by [tex] v= v_0 + at [/tex] with [tex]x_0[/tex] and [tex]v_0[/tex] being the position and velocity at [tex]t=0[/tex]s.
By comparing the two acceleration is costant, and it's the same at t=0, t=3.0, or t=3000s, and is [tex]\frac 1 2 a = 4.1[/tex]. Velocity comes from the second formula, you found the acceleration in the previous step, and you just have to plug 0 for [tex]v_0[/tex], the value of a you found, and 6 s for t.
