A roller coaster starts from a deck at an elevation of 20 feet above the ground. On the first hill it climbs 83 feet and then drops 42 feet. On the second hill the coaster climbs 128 feet and then drops 90 feet. How far above the ground is the coaster after the second hill?
I would say 99 feet. An elevation of 20 feet above the ground is the starting point. Then as the coaster rises 83 feet, you add 20 + 83 = 103 feet. Then it drops 42 feet. 103 - 42 = 61 feet. Then it rises 128 feet on the second hill. 61 + 128 = 189 feet. Finally, it drops 90 feet. 189 - 90 = 99 feet above the ground after the second hill.
