Angel Johnson $($Social Security number $111-11-1111)$ is $39$ years old and is married to Robin Johnson $($Social Security number $123-45-6789).$ The Johnsons live at $16512$ Old Ferry Road, Norfolk VA $23661.$ They file a joint return and have two dependent children, Carrie, age $17,$ and Noah, age $18.$ Carrie$$s Social Security number is $123-45-6788,$ and Noah$$s Social Security number is $123-45-6787.$ In $2021,$ Angel and Robin had the following transactions:

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Robin $$120,000$ in salary from Magnet Corporation, where she is a project manager. Withholding for Federal income tax was $$10,750.$ The amounts withheld for FICA taxes were as follows: $$7,049($$$113,700$ X $6\mathrm{.}2\%)$ for Social Security and $$1,740($$$120,000$ X $1\mathrm{.}45\%)$ for Medicare. Robin worked in Mexico from January $1,2020,$ until February $15,2021.$ Her $$120,000$ salary for $2021$ includes $$18,000$ she earned for January and one$-$half of February $2021$ while working in Mexico.

Angel and Robin received $$400$ interest on Fairfax County $($Virginia$)$ school bonds.

Angel received $$2,300$ interest from a Bermuda bank account.

Robin received $50$ shares of Starbucks Corporation common stock as a stock dividend. The shares had a fair market value of $$3,500$ at the time Robin received them, and she did not have the option of receiving cash.

Angel and Robin received a $$1,200$ refund on their $2020$ Virginia income taxes. Their itemized deductions in $2020$ totaled $$34,000$ and included state taxes of $$7,400.$

Robin paid $$6,600$ alimony to her former husband, James Alexander $($Social Security number $123-45-6786).$ The divorce was finalized in March $2016.$

Angel and Robin kept the receipts for their sales taxes paid of $$1,100.$

Angel and Robin$$s itemized deductions were as follows:

$-$State income tax paid and withheld totaled $$5,100.$

$-$Real estate taxes on their principal residence were $$3,700.$

$-$Mortgage interest on their principal residence was $$2,500.$

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Part $1-$ Tax Computation

Compute the Johnsons$$ net tax payable $($or refund due$)$ for $2021.$

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Part $2-$Tax Planning

The Johnsons are considering buying another house. Their house mortgage payments would increase by $$500($to $$1,500)$ per month, which includes a $$250$ increase in interest and a $$100$ increase in property tax. The Johnsons would like to know how much the mortgage payments would increase net of any change in their income tax. Write a letter to the Johnsons that contains your advice.