Question

The weight of an object follows the equation w=Cr^-2, where C is the constant and r is the distance the object is from the center of the earth.
a. solve the equation for r.
b. Suppose the object is 100 pounds when at sea level. Find the value of C that makes the equation true. Sea level is 3,963 miles from the center of the earth.
c. Use the value of C you found to determine how much the object would weigh in Death Valley ( 282 feet below sea level) and The top of Mount Mc Kinley (20,320 feet above sea level)
I'm struggling with how to set these up. Any help?