Read the following information carefully and asnwer the question which follows:
'A×B' means 'A is father of B'.
'A+ B' means 'A is the daughter of B'.
'A÷B' means 'A is the son of B'.
'A−B' means 'A is the sister of B'.'
What will come in place of the question mark, to eatablish that 'P'is the son-in-law of 'S' in the following expression?
'P×Q + R −T? S