Diana left home at 10.30 a.m. and drove towards the countryside. 3 hours later, her younger brother left their home and drove towards the same countryside at 93 km/h. When the younger brother reached the countryside at 6.30 p.m., Diana had another 3 km to travel. What was Diana’s average speed? Express your answer in mixed number.
Time that the Diana's younger brother started driving = 1.30 p.m.
Duration that Diana's younger brother drove from 1.30 p.m. to 6.30 p.m. = 5 h

Distance that Diana's younger brother travelled
= 5 x 93
= 465 km

Distance that Diana travelled by the time her younger brother reached the city
= 465 - 3
= 462 km

Time that Diana took to travel 462 km = 8 h

Diana's average speed
= 462 ÷ 8
= 57³₄ km/h

Answer(s): 57³₄ km/h