Answer:
The expanding accounting equation is:
Assets = Liabilities + Stockholders Equity 
                                  [Common Stock + Retained Earnings]
                                                                (Revenues - Expenses - Dividends)
Now, we replace the amounts in the formula
$84,325 = $2,560 + X
                               [  X  + R ]
                              ($54,780 - $28,125 - $13,450)
$84,325 = $2,560 + X
                               [  X  + R ]
                              ($54,780 - $28,125 - $13,450)
$84,325 = $2,560 + X
                               [  X  + $13,205 ]
$84,325 = $2,560 + X
                                [  68,560  + $13,205 ]
$84,325 = $2,560 + $81,765
Both sides are now equal to $84,325
Thus, Common Stock = $68,560