$${\sqrt{{\mathtt{12\,007\,900\,001}}}} = {\mathtt{109\,580.563\: \!974\: \!639\: \!225\: \!252\: \!4}}$$
-6/12 - 11/12 could be either -17/12 or -1 5/12
It's simple. You multiply $400 by 20% then add the number you get to $400.
400*.20=
Add the number you get from that back to 400 and that is your answer.
$480
