Gwen left home at 11.45 a.m. and drove towards the seaside resort. 2 hours later, her younger sister left their home and drove towards the same seaside resort at 97 km/h. When the younger sister reached the seaside resort at 4.45 p.m., Gwen had another 6 km to travel. What was Gwen’s average speed? Express your answer in mixed number.
Time that the Gwen's younger sister started driving = 1.45 p.m.
Duration that Gwen's younger sister drove from 1.45 p.m. to 4.45 p.m. = 3 h

Distance that Gwen's younger sister travelled
= 3 x 97
= 291 km

Distance that Gwen travelled by the time her younger sister reached the city
= 291 - 6
= 285 km

Time that Gwen took to travel 285 km = 5 h

Gwen's average speed
= 285 ÷ 5
= 57 km/h

Answer(s): 57 km/h