According to the given requirements, the length (the run) of the ramp should be at least 12 times the height (the rise). It means that the run must be at least 12 * 12 = 144 inches, or= 12 feet. ANSWER In terms of percentage, the grade of the ramp (which term is the same as the slope) is the grade of the ramp = the rise divided by the run <= = 8.33%. ANSWER