Work is a derived physical quantity. Its unit is Joule.

Mathematically, Work = Force x displacement.

So, Joule is the product of Newton (N) and metre (m). Again, Newton is a derived unit of Force and is equal $\rm kgms^{-2}$.

Hence,

Joule (J) = $\rm kgms^{-2} \cdot m = kg m^2s^{-2}$.

Clearly, Joule depends upon three fundamental physical quantities, i.e., kilogram (kg), metre (m), and second (s). Hence, it is the derived unit of work.