Maggie's Muffins Bakery generated $$4$ million in sales during $2019,$ and its year$-$end total assets were $$2\mathrm{.}8$ million. Also, at year$-$end $2019,$ current liabilities were $$1$ million, consisting of $$300,000$ of notes payable, $$500,000$ of accounts payable, and $$200,000$ of accruals. Looking ahead to $2020,$ the company estimates that its assets must increase at the same rate as sales, its spontaneous liabilities will increase at the same rate as sales, its profit margin will be $5\%,$ and its payout ratio will be $70\%.$

How large a sales increase can the company achieve without having to raise funds externally$$that is$,$ what is its self$-$supporting growth rate? e$.$g$.$ Sales can increase by $ x $,$ that is by x $\%.$