Gem left home at 11.30 a.m. and drove towards the seaside resort. 2 hours later, her mother left their home and drove towards the same seaside resort at 100 km/h. When the mother reached the seaside resort at 4.30 p.m., Gem had another 4 km to travel. What was Gem’s average speed? Express your answer in mixed number.
Time that the Gem's mother started driving = 1.30 p.m.
Duration that Gem's mother drove from 1.30 p.m. to 4.30 p.m. = 3 h

Distance that Gem's mother travelled
= 3 x 100
= 300 km

Distance that Gem travelled by the time her mother reached the city
= 300 - 4
= 296 km

Time that Gem took to travel 296 km = 5 h

Gem's average speed
= 296 ÷ 5
= 59¹₅ km/h

Answer(s): 59¹₅ km/h