Suppose that a particle moves according to the law of motion
(A) Find the velocity at time $t$.

$v(t) =$
(B) What is the velocity after 3 seconds?

Velocity after 3 seconds =
(C) Find all values of $t$ for which the particle is at rest. (If there are no such values, enter 0. If there are more than one value, list them separated by commas.)

$t$ =
(D) Use interval notation to indicate when the particle is moving in the positive direction. (If the particle is never moving in the positive direction, enter "{}" without the quotation marks.)