Alot as far as i know unless you need it in formal terms.
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:
Answer: 4 x 106
That’s how you write forty million in scientific notation.