I would like to know if it would be m/s² or just m/s and explain why. thanks

It will be
[tex] {m/s}^{2} [/tex]
I am just explaining with the units only, because you want to know the accurate unit.
[tex] \frac{m/s}{s} \\ = \frac{m}{s} \times \frac{1}{s} \\ = \frac{m}{s \times s} \\ = \frac{m}{ {s}^{2} } \\ = {m/s}^{2} [/tex]
Hope you understood.
Do comment if you have any query.