
Answer:
General Journal             Debit        Credit
Amortization expenses     $6,000,000
   Patent                            $6,000,000
Calculation of annual amortization after the estimate change
Cost                      $21,600,000
Less: Amortization till date    $9,600,000
     ($2,400,000*4 years)
Un-amortized Cost A Â Â Â Â Â Â Â Â $12,000,000
Remaining Life (6yrs-4yrs)       2 Years  Â
New annual amortization     $6,000,000
Old annual amortization = $21,600,000 / 9 years = $2,400,000
Amortization till date = $2,400,000 * 4 = $9,600,000