Please explain step by step

19. The percentage of a certain country's national income generated by nonfarm proprietors may be modeled by the following formula, where x is the number of years since 1962. According to this model, in what year from 1962 through 1992 was this percentage a minimum? Calculate the answer, and then check it on the graph. p(x) = 14x - 240x2- 2461x + 584,775 80,784 In the year the percentage was at a minimum. (Type a whole number.)