Linda left home at 11.40 a.m. and drove towards the city. 2 hours later, her younger sister left their home and drove towards the same city at 85 km/h. When the younger sister reached the city at 5.40 p.m., Linda had another 4 km to travel. What was Linda’s average speed? Express your answer in mixed number.
Time that the Linda's younger sister started driving = 1.40 p.m.
Duration that Linda's younger sister drove from 1.40 p.m. to 5.40 p.m. = 4 h

Distance that Linda's younger sister travelled
= 4 x 85
= 340 km

Distance that Linda travelled by the time her younger sister reached the city
= 340 - 4
= 336 km

Time that Linda took to travel 336 km = 6 h

Linda's average speed
= 336 ÷ 6
= 56 km/h

Answer(s): 56 km/h