I don’t know how to do these

Acircle has a diameter will endpoints of (-2,8) and (6, 4). what is the center of the circle

How many $20 bills do you need to have to make $280

Twenty points. suppose that one doll house uses the 1 inch scale, meaning that 1 inch on the doll house corresponds to 1/2 foot for life-sized objects. if the doll house is 108 inches wide, what is the width of the full-sized house that it's modeled after? in inches and feet