Joe's Burgers would like to maintain their cash account at a minimum level of $$300,000,$ but expects the standard deviation in net daily cash flows to be

$$20,000$; the effective annual rate on marketable securities to be $5\mathrm{.}2$ percent per year; and the trading cost per sale or purchase of marketable securities to

be $$22\mathrm{.}50$ per transaction. What will be their optimal upper cash limit$?$