Kimberly left home at 10.50 a.m. and drove towards the seaside resort. 3 hours later, her younger brother left their home and drove towards the same seaside resort at 88 km/h. When the younger brother reached the seaside resort at 6.50 p.m., Kimberly had another 4 km to travel. What was Kimberly’s average speed? Express your answer in mixed number.
Time that the Kimberly's younger brother started driving = 1.50 p.m.
Duration that Kimberly's younger brother drove from 1.50 p.m. to 6.50 p.m. = 5 h

Distance that Kimberly's younger brother travelled
= 5 x 88
= 440 km

Distance that Kimberly travelled by the time her younger brother reached the city
= 440 - 4
= 436 km

Time that Kimberly took to travel 436 km = 8 h

Kimberly's average speed
= 436 ÷ 8
= 54¹₂ km/h

Answer(s): 54¹₂ km/h