Why do we have different units for the same physical quantity?

In the following equations, the distance $x$ is in $\mathrm{meters}$, the time $t$ in $\mathrm{seconds}$ and the velocity $v$ in $\mathrm{m} {\mathrm{s}}^{-1}$. What is the SI unit of the constant $C_1$ and $C_2$$?$

(a) $v^2=2C_{1}x$

(b) $x=C_1\cos C_{2}t$

(c) $v=C_1{e}^{-C_{2}t}$