In a certain code language, 'x' represents '+', '÷' represents 'x', '-' represents '÷' and '+' represents '-'. Find out the answer to the following question.
Raman remembers that his marriage is before 20th July and after 13th July. His mother remembers that Raman’s marriage is after 16th July. His father remembers that Raman’s marriage is before 19th July. On which date of July is Raman’s marriage?