a. The total time taken for the entire journey is the sum of time taken for each journey. But Average speed = \(\frac { total distance covered}{ time taken}\) then Time taken = \(\frac { total distance covered}{ time taken}\) for the first journey(t1), d = 112km and speed = 70km/hr \(t_1 = \frac{112}{70} = \frac{8}{5}\)hrs for the second journey(t2), distance = 60km and speed = 50km/hr \(t_2 = \frac{60}{50} = \frac{6}{5}\)hrs Therefore, Total time taken = \( t_1 + t_2 = \frac{8}{5} + \frac{6}{5}\) = 2.8hrs. b. if \(\frac{x}{y}\) = 2 , then x = 2y and if \(\frac{y}{z}\) = 3 then z = \(\frac{y}{3}\), substituting, the values of x and z into \(\frac{ x + y}{y + z }\) = \(\frac{2y + y}{y + \frac{y}{3}} = 3y\div\frac{4y}{3} = 3y\times\frac{3}{4y} = \frac{9}{4}\) Therefore, \(\frac{ x + y}{y + z } = \frac{9}{4}\)