(d) Let the total number of quizzes = x and score of previous quizzes = y ∴xy+97​=90,xy+70​=87⇒xy​+x97​=90,xy​+x70​=87⇒xy​=90−x97​ ........(i)⇒xy​=87−x70​..........(ii)From (i) and (ii)∴90−x97​=87−x70​3=x−70​+x97​=x27​