1. The problem statement, all variables and given/known data Erik’s disabled sailboat is floating stationary 3 miles East and 2 miles North of Kingston. The sailboat has a radar scope that will detect any object within 3 miles of the sailboat. A ferry leaves Kingston heading toward Edmonds at 12 mph. Edmonds is 6 miles due east of Kingston. After 20 minutes the ferry turns heading due South. Ballard is 8 miles South and 1 mile West of Edmonds. Impose coordinates with Ballard as the origin. When does the ferry enter the radar zone? 2. Relevant graph 3. The attempt at a solution I wanted ask if the distance to the origin has to be an absolute value in these kind of problems? If the equation of a circle is (x-h)^2+(y-k)^2=r^2 with h and k being the coordinates of the center of a circle, then if I x=-5, h=-2 I am going to have -5+2=-3 and get negative values (for time) with this equation ((-5+2)-12t)^2+(8-10)^2=9. It only works if the value is positive (absolute): ((|-5+2|)-12t)^2+(8-10)^2=9, or I guess then it should look like this ((|-5+2|)-12t)^2+(|8-10|)^2=9 Also another totally silly question: where does this 12t come from? As I understand it sets the whole thing in motion but I don't quite see how it's legal, if x and h are already set in the equation. I referenced another similar problem and that's why I don't completely understand all the steps.