Shirley is twenty years old. She wants to retire at the age of $60$ with a monthly income of $$8,000.$ She expects to live to $85.$ She has $$50,000$ invested in her retirement savings account today. If she can earn $7\%,$ compounded monthly, on her investments, both before and after retirement, how much must she save, every month, for the next $40$ years?

$[$Answers: Round to the nearest dollar with no $ symbol; e$.$g$.$ $$123\mathrm{.}45=123]$

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