How do you solve this physics problem?

Question

A $3000\,\rm kg$ car travels at a velocity of $6.00\,\rm m/s$ due north then accelerates at $3.00\,\rm m/s^2$ due south. What is the velocity of the car after $1.50$ seconds?

Answer 1

If we define North as positive, then South direction would be the negative direction. From the definition of acceleration, we can find the magnitude of final velocity:

$$a=\dfrac{v-u}{t} \iff v=u+at$$

$$\begin{bmatrix}a \\ u \\ t \end{bmatrix}=\begin{bmatrix}-3\ m/s^2\\+6\ m/s \\ 1.5 \ s\end{bmatrix}\implies v=+6-3\cdot1.5=+1.5 \ m/s$$

Final velocity is $+1.5 \ m/s$ which means $1.5 \ m/s$ due North.