Difference is represented by the subtraction of 2 numbers. If we want to represent the difference of 2 numbers, we need to subtract one number from the other number.
There is 1 quiz with score 1, so 1 point; 3 quizzes with score 2 for 3*2 = 6 points; 4 quizzes with score 3 for 4*3 = 12 points; 4 quizzes with score 4 for 4*4 = 16 points; and 1 quiz with score 5 for 5 points.