How many T's are there in the following sequence which are immediately preceded by P but not imeediately followed b S ? S T P Q T S P T R P T S R P S T Q P T R P T M P T S
A + B means A is the son of B; A - B means A is the wife of B; A x B means A is the brother of B; A ÷ B means A is the mother of B; and A = B means A is the sister of B. What does P + R - Q mean ?