Why is the correct answer 7. After the 3rd plate of sushi doesn't Professor Carrell only gain 19 dollars of benefit. So he would stop at a point only when the benefit is greater than the cost?

Question 15 0 / 6 pts The below graph show's Professor Carrell's Total Benefit for eating plates of sushi at Nami's "all you can eat" sushi, which costs $20. Plates of Sushi Total Benefit ($) 1 21 41 W N 59 74 UT P 85 6 91 7 91 81 How many plates of Sushi does professor Carrell eat? Correct Answer 07 0 8 You Answered 1 O 2