Since the term -(x-7)^2 is negative, the largest height that the ball can reach is when this term is 0. 0+20=20, meaning that the highest the ball can go is 20 feet. Hope this helps!
Range is the difference between the largest and the smallest variable. If the range is 18 and the smallest number is 9. Add 9 to 18. 9+18= 27. 27 is the largest number.