Answer
The product $RC$ has units of $s$
Work Step by Step
We know that capacitance $C = \frac{Q}{V}$, so capacitance can be expressed in units of $\frac{C}{V}$, (where $C$ is units of coulombs)
We know that resistance $R = \frac{V}{I}$, so resistance can be expressed in units of $\frac{V}{A}$
We can find the units of $RC$:
$\frac{C}{V}\times \frac{V}{A} = \frac{C}{A} = \frac{C}{C/s} = s$
