The dog is chasing you in the circular pattern clockwise. You are running at 30ft/sec and dog is keeping the pace. Circle has the radius of 300 ft. In the meantime the dad is armed and prepared to take out mut with the slingshot, and is situated 1000ft to southeast from center of circle, watching as you approach. To make the direct hit dad requires to know how fast distance between dog and himself is changing when dog is precisely 900ft from him. Use calculus to find out.