In the year 2035, Uber produces rides using self-driving cars (S) and human drivers (D). Drivers cost $24/hour and self-driving cars cost $50/hour. Ubers hourly production of rides is given by (,)=^2/31(2/3). Calculate Ubers marginal rate of technical substitution between self-driving cars and human drivers when =55 and =25, putting the marginal product of self-driving cars in the numerator.