Usha left home at 11.15 a.m. and drove towards the countryside. 2 hours later, her younger brother left their home and drove towards the same countryside at 88 km/h. When the younger brother reached the countryside at 4.15 p.m., Usha had another 4 km to travel. What was Usha’s average speed? Express your answer in mixed number.
Time that the Usha's younger brother started driving = 1.15 p.m.
Duration that Usha's younger brother drove from 1.15 p.m. to 4.15 p.m. = 3 h

Distance that Usha's younger brother travelled
= 3 x 88
= 264 km

Distance that Usha travelled by the time her younger brother reached the city
= 264 - 4
= 260 km

Time that Usha took to travel 260 km = 5 h

Usha's average speed
= 260 ÷ 5
= 52 km/h

Answer(s): 52 km/h