Tokyo Olympic Games. Giselle Nolan had planned her trip to the Olympic Games in Tokyo, Japan, for many months. She had budgeted$-$saved$-$USD$15,800$ for expenses while in Tokyo. Giselle had waited till the last minute, however, to exchange the dollars for Japanese yen $($JPY$),$ doing it in the San Francisco airport in the United States on July $30$ at JPY$109\mathrm{.}52=1\mathrm{.}00$USD. Given the following average exchange rates in the spring and summer of $2021,,$ when should she have exchanged the dollars for yen to maximize her Tokyo spending money?