If $\mathbf{r} (t) = \cos (-6 t) \mathbf{i} + \sin (-6 t) \mathbf{j} + 2 t \mathbf{k}$, compute:

A. The velocity vector $\mathbf{v} (t) =$ $\mathbf{i} +$ $\mathbf{j} +$ $\mathbf{k}$

B. The acceleration vector $\mathbf{a} (t) =$ $\mathbf{i} +$ $\mathbf{j} +$ $\mathbf{k}$

Note: the coefficients in your answers must be entered in the form of expressions in the variable $t$; e.g. "5 cos(2t)"