Rachel leased an apartment to Bertha for a one-year term beginning May 1, at $800 a month, "payable in advance on the first day of each and every month of said term." At the time the lease was signed, Bertha told Rachel that she received her salary on the tenth of the month, and that she would be unable to pay the rent before that date each month. Rachel replied that would be satisfactory. On June 2, Bertha not having paid the June rent, Rachel sued Bertha for the rent. At the trial, Bertha offered to prove the oral agreement as to the date of payment each month. Explain whether Rachel should succeed.