Sabrina left home at 10.50 a.m. and drove towards the city. 3 hours later, her mother left their home and drove towards the same city at 81 km/h. When the mother reached the city at 6.50 p.m., Sabrina had another 5 km to travel. What was Sabrina’s average speed? Express your answer in mixed number.
Time that the Sabrina's mother started driving = 1.50 p.m.
Duration that Sabrina's mother drove from 1.50 p.m. to 6.50 p.m. = 5 h

Distance that Sabrina's mother travelled
= 5 x 81
= 405 km

Distance that Sabrina travelled by the time her mother reached the city
= 405 - 5
= 400 km

Time that Sabrina took to travel 400 km = 8 h

Sabrina's average speed
= 400 ÷ 8
= 50 km/h

Answer(s): 50 km/h