Irene left home at 11.15 a.m. and drove towards the province. 3 hours later, her younger brother left their home and drove towards the same province at 99 km/h. When the younger brother reached the province at 7.15 p.m., Irene had another 3 km to travel. What was Irene’s average speed? Express your answer in mixed number.
Time that the Irene's younger brother started driving = 2.15 p.m.
Duration that Irene's younger brother drove from 2.15 p.m. to 7.15 p.m. = 5 h

Distance that Irene's younger brother travelled
= 5 x 99
= 495 km

Distance that Irene travelled by the time her younger brother reached the city
= 495 - 3
= 492 km

Time that Irene took to travel 492 km = 8 h

Irene's average speed
= 492 ÷ 8
= 61¹₂ km/h

Answer(s): 61¹₂ km/h