Lynn left home at 11.20 a.m. and drove towards the city. 2 hours later, her younger brother left their home and drove towards the same city at 75 km/h. When the younger brother reached the city at 6.20 p.m., Lynn had another 4 km to travel. What was Lynn’s average speed? Express your answer in mixed number.
Time that the Lynn's younger brother started driving = 1.20 p.m.
Duration that Lynn's younger brother drove from 1.20 p.m. to 6.20 p.m. = 5 h

Distance that Lynn's younger brother travelled
= 5 x 75
= 375 km

Distance that Lynn travelled by the time her younger brother reached the city
= 375 - 4
= 371 km

Time that Lynn took to travel 371 km = 7 h

Lynn's average speed
= 371 ÷ 7
= 53 km/h

Answer(s): 53 km/h