Please help! this is due in an hour

Acircular city park has a sidewalk directly through the middle that is 111 - feet long. if each bag of fertilizer covers 50 square feet, then determine how many bags of fertilizers the parks and recreation department needs to use to cover the circular park. ignore all the sidewalks around and through the park.

Credit card a offers an introductory apr of 3.4% for the first three months and standard apr of 15.7% thereafter,

How can i differentiate this equation?