need help with this

Question

 On your cousin’s quinceañera day you leave for the church 30.0 min before the quince is to begin, which should leave plenty of time since the church is only 17.0 km away. On the way. However, you have to make an unanticipated stop because of road construction work. As a result, your average speed for the first 15 min is only 12.0 km/hr. What average speed do you need to have on the remainder of the trip to get you to the church on time? 

Answer 1

First 15 min [.25 hr] so .25 x 12 = 4km so 13km to travel in 15 min [.25hr] 13/.25 = 52km/hr to make it on time.