Answer
$\vec{v}(t) = 3{i}-(8)t\hat{j}$
Work Step by Step
We're given;
$\vec{r}(t) = 3t\,\hat{i}-4t^2\hat{j}+2\,\hat{k}$
We know the velocity is the derivative of the displacement vector. We can thus find $\vec{v}$ by taking derivatives of $\vec{r}$ component-wise:
$\vec{v}(t) = 3{i}-(8)t\hat{j}$
