Betty left home at 11.20 a.m. and drove towards the seaside resort. 3 hours later, her grandmother left their home and drove towards the same seaside resort at 98 km/h. When the grandmother reached the seaside resort at 7.20 p.m., Betty had another 6 km to travel. What was Betty’s average speed? Express your answer in mixed number.
Time that the Betty's grandmother started driving = 2.20 p.m.
Duration that Betty's grandmother drove from 2.20 p.m. to 7.20 p.m. = 5 h

Distance that Betty's grandmother travelled
= 5 x 98
= 490 km

Distance that Betty travelled by the time her grandmother reached the city
= 490 - 6
= 484 km

Time that Betty took to travel 484 km = 8 h

Betty's average speed
= 484 ÷ 8
= 60¹₂ km/h

Answer(s): 60¹₂ km/h