To what potential should you charge a 3.0 μf capacitor to store 1.0 j of energy?

The energy stored in a capacitor is given by:

where
U is the energy
C is the capacitance
V is the potential difference

The capacitor in this problem has capacitance

So if we re-arrange the previous equation, we can calculate the potential V that should be applied to the capacitor to store U=1.0 J of energy on it:

So what is the question