Risa left home at 11.40 a.m. and drove towards the suburb. 2 hours later, her cousin left their home and drove towards the same suburb at 95 km/h. When the cousin reached the suburb at 6.40 p.m., Risa had another 6 km to travel. What was Risa’s average speed? Express your answer in mixed number.
Time that the Risa's cousin started driving = 1.40 p.m.
Duration that Risa's cousin drove from 1.40 p.m. to 6.40 p.m. = 5 h

Distance that Risa's cousin travelled
= 5 x 95
= 475 km

Distance that Risa travelled by the time her cousin reached the city
= 475 - 6
= 469 km

Time that Risa took to travel 469 km = 7 h

Risa's average speed
= 469 ÷ 7
= 67 km/h

Answer(s): 67 km/h