Betty left home at 10.45 a.m. and drove towards the province. 3 hours later, her grandmother left their home and drove towards the same province at 90 km/h. When the grandmother reached the province at 6.45 p.m., Betty had another 2 km to travel. What was Betty’s average speed? Express your answer in mixed number.
Time that the Betty's grandmother started driving = 1.45 p.m.
Duration that Betty's grandmother drove from 1.45 p.m. to 6.45 p.m. = 5 h

Distance that Betty's grandmother travelled
= 5 x 90
= 450 km

Distance that Betty travelled by the time her grandmother reached the city
= 450 - 2
= 448 km

Time that Betty took to travel 448 km = 8 h

Betty's average speed
= 448 ÷ 8
= 56 km/h

Answer(s): 56 km/h