This is a classic retained earnings question right out of the textbook
The general equation can be expressed as following:
Ending Retained Earnings = Beginning Retained Earnings - Investments - Dividends Paid + Net Income
That said, lets deal with the question:
$420,000 + $63,000 - $125,000 - $55,000 = $303,000
Other data given in this question is irrelevant!