Question 12
When Albert begins walking up slope $AB$ (1 km distance), across level ground $BC$ (12 km distance), and down slope $CD$ (3 km distance), Daniel begins his journey in the opposite direction from $D$ at the same time. Given that the speeds of both travelling up the slope, on level ground and down slope are 2 km/h, 4 km/h and 5 km/h respectively, find the number of hours that has passed when they meet.
