Mookie, Gandalf, and O’Malley are selling tickets to a play. Gandalf sold five less than three times the number of tickets Mookie sold. O’Malley sold one more than seven times the number of tickets Mookie sold. The number of tickets O’Malley sold is four more than twice the number of tickets that Mookie and Gandalf sold together. How many tickets did they sell in total?

The standard forrm equation of the circle is (x-h)² + (y-k)² = r²
where h,k : x,y-coordinate of the center
           r : radius of the circle
Get the center of the circle : h = (x1 + x2)/2 = (9+5)/2 = 7
                                             k = (y1 + y2)/2 = (4+2)/2 = 3
=> the center is (7,3)
Because the given information gave 2 endpoints so we can choose one of these, then use the distance formula to get the radius
                                            r = √(x1 - h)² + (y1 - k)²
                                            r = √(9 - 7)² + (4 - 3)²
                                            r = √2² + 1² 
                                            r = √5
Finally, the equation of the circle is (x - 7)² + (y - 3)² = (√5)²
                                                        (x - 7)² + (y - 3)² = 5