**P. 4617.** A student went by bicycle to Saddle City from Frame Village. He planned to go with an average speed of 18 km/h. Because of the heavy traffic, in the first third of his journey his average speed was only 15 km/h.

*a*) What should his average speed be in the remaining part of his journey, if he is to arrive at the planned time?

*b*) What should his average speed be in the remaining time, if his speed was 15 km/h in the first one-third of the time of his journey?

(4 points)

**Deadline expired on 10 April 2014.**

\(\displaystyle b)\) 19,5 km/h.