The ski club is planning a trip for winter break. They write the equation C=200+10N to estimate the cost in dollars, C of the trip for N students.

Duncan and Corey both use the equation to estimate the cost for 50 students. Duncan says the cost is $10,500 , and Corey says it's $700.

AWhose estimate is correct?
BHow do you think Duncan and Corey found such different estimates if they used the same equation?