The answer is B. The diagram shows that n is the difference between the total number of children who rode Twister on Friday and Saturday, so the answers A and D are excluded. The answer C is not true because there were just 165 boys (not 367 + 165) and 218 girls who rode Twister.

thankyou for your help...I have a question... how do you know N stands for the difference between the total number of children who rode twister on Friday and Saturday