Answer
We need an additional capacitor of $20~\mu F$ combined in parallel with the $30~\mu F$ capacitor.
Work Step by Step
If we combine another capacitor with the $30~\mu F$ capacitor in series, then the equivalent capacitance is less than $30~\mu F$.
If we combine another capacitor with the $30~\mu F$ capacitor in parallel, then the equivalent capacitance is greater than $30~\mu F$.
Therefore, we need to combine another capacitor in parallel.
When we combine two capacitors in parallel, the equivalent capacitance is the sum of the two capacitors. To produce an equivalent capacitance of $50~\mu F$, we need an additional capacitor of $20~\mu F$ combined in parallel with the $30~\mu F$ capacitor.
