Aparticle moves along the x-axis according to the equation x(t)= 2.9- 4.1t^2 m. what are the velocity (in m/s) and acceleration (in m/s^2) at t=3.0 s and t=6.0 s

From the equation you can tell that your particle is moving with a costant acceleration. The generic movement equation is , and velocity is given by with and being the position and velocity at s.

By comparing the two acceleration is costant, and it's the same at t=0, t=3.0, or t=3000s, and is . Velocity comes from the second formula, you found the acceleration in the previous step, and you just have to plug 0 for , the value of a you found, and 6 s for t.

i believe the answer is a