Now that she is selling mixers and her customers can use credit cards to pay for them, Natalie is thinking of upgrading her website to include the online sale of mixers and payment by credit card. This would enable her to sell these mixers to a wider range of customers using the Internet. Natalie contacts her brother who originally prepared the website for her. He agrees to upgrade the site so it can handle credit card security issues as well as direct order entry. The cost of the upgrade is $1,800. This cost would be incurred and paid for during the month of August 2024, and the upgrade would be operational September 1, 2024. Recall that Natalie's website had an original cost of $600 and is being amortized using the straight- line method over 24 months, starting December 1,2023 , with zero residual value. Additional costs for website maintenance and insurance are estimated to be $1,200 per year. If Natalie decides to upgrade the website, its useful life will not change and there will be no change in residual value. (a) Prepare the journal entry to record the upgrade. (List all debit entries before credit entries. Credit account titles are automatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for the account titles and enter 0 for the amounts.) Calculate the monthly amortization expense before the upgrade and the accumulated amortization and book value on August 31 2024. Monthly amortization Accumulated amortization Book value (c) Calculate the revised monthly amortization expense as of September 1, 2024. Revised monthly amortization