Answer
The required potential difference is $~~10\times 10^6~V$
Work Step by Step
We can find the required potential difference:
$K = q~V$
$V = \frac{K}{q}$
$V = \frac{20~MeV}{2e}$
$V = \frac{20\times 10^6~eV}{2e}$
$V = 10\times 10^6~V$
The required potential difference is $~~10\times 10^6~V$
