Holt Developments Ltd$.$ put an asset in service on January $1,2021.$ Its cost was $$504,000,$ its predicted service life was six years, and its expected residual value was $$50,400.$ The company decided to use double$-$declining$-$balance depreciation. After consulting with the company$$s auditors, management decided to change to straight$-$line depreciation in $2023,$ without changing either the original service life or residual value.

Required:

a$.$ What is depreciation expense for $2023?$

b$.$ Calculate the effect of this change on retained earnings.