h represents the amount of hamburgers. 3h is equivalent to c, since we know that the number of cheeseburgers cold was three times the number of hamburgers sold. We add the two because it is a combined total.
Now we input the value for t, which is the total number of hamburgers and cheeseburgers sold, which is 516.
The total number of degrees in a triangle is 180. Since both sides of the triangle are the radius of the circle, the triangle is isosceles. Therefore the two opposite angles are equal. Thus, the central angle is 180° − 2(20°) = 140°.