Lynn left home at 10.40 a.m. and drove towards the countryside. 3 hours later, her grandmother left their home and drove towards the same countryside at 86 km/h. When the grandmother reached the countryside at 6.40 p.m., Lynn had another 2 km to travel. What was Lynn’s average speed? Express your answer in mixed number.
Time that the Lynn's grandmother started driving = 1.40 p.m.
Duration that Lynn's grandmother drove from 1.40 p.m. to 6.40 p.m. = 5 h

Distance that Lynn's grandmother travelled
= 5 x 86
= 430 km

Distance that Lynn travelled by the time her grandmother reached the city
= 430 - 2
= 428 km

Time that Lynn took to travel 428 km = 8 h

Lynn's average speed
= 428 ÷ 8
= 53¹₂ km/h

Answer(s): 53¹₂ km/h