Slope = Δy/Δx or rise/run. Consider where the balloon was tied to be x = 0. The balloon is 65 ft to the right of where it was tied, so now x = 65 ft. The horizontal change or run = 65 ft. Given that the ground is y = 0, when the balloon is at 20 ft, the vertical change or rise = 20 ft. so rise/run = 20 ft/65 ft = 0.308 or about 0.31.