When Valerie is reaching 1/4 of the distance between library and Mall P, Celine is 2km ahead of her.
So, when Valerie reaches the library, Celine will be 8km past the library.
When it is 20 mins,
-Valerie will reach the library.
-Celine will be 8km past the library. She is 15km (23 – 8) from Mall Q.
Celine reaches Mall Q in 32 mins. So, celine covers this distance 15km in 12mins (32 – 20)
Celine speed = 15 km / 12 mins = 15 / 0.2hr = 75 km/hr.