Can someone please help me with these questions :)

Acircle has a radius of 5/6 units and is centered at (3.6, 7.8) write the equation of this circle

Precalculus question, image attached.

Luigi is the first person to finish a 5k race and is standing 13 feet beyond the finish line. another runner, mario, is still running the race and has approximately 24 feet before he reaches the finish line. what is the distance between mario and luigi? explain through words, numbers or pictures how you found the answer.