Emma left home at 11.45 a.m. and drove towards the seaside resort. 2 hours later, her younger brother left their home and drove towards the same seaside resort at 91 km/h. When the younger brother reached the seaside resort at 5.45 p.m., Emma had another 4 km to travel. What was Emma’s average speed? Express your answer in mixed number.
Time that the Emma's younger brother started driving = 1.45 p.m.
Duration that Emma's younger brother drove from 1.45 p.m. to 5.45 p.m. = 4 h

Distance that Emma's younger brother travelled
= 4 x 91
= 364 km

Distance that Emma travelled by the time her younger brother reached the city
= 364 - 4
= 360 km

Time that Emma took to travel 360 km = 6 h

Emma's average speed
= 360 ÷ 6
= 60 km/h

Answer(s): 60 km/h