Hilda left home at 10.50 a.m. and drove towards the seaside resort. 3 hours later, her grandfather left their home and drove towards the same seaside resort at 98 km/h. When the grandfather reached the seaside resort at 6.50 p.m., Hilda had another 4 km to travel. What was Hilda’s average speed? Express your answer in mixed number.
Time that the Hilda's grandfather started driving = 1.50 p.m.
Duration that Hilda's grandfather drove from 1.50 p.m. to 6.50 p.m. = 5 h

Distance that Hilda's grandfather travelled
= 5 x 98
= 490 km

Distance that Hilda travelled by the time her grandfather reached the city
= 490 - 4
= 486 km

Time that Hilda took to travel 486 km = 8 h

Hilda's average speed
= 486 ÷ 8
= 60³₄ km/h

Answer(s): 60³₄ km/h