Help about finding PEAK HOUR Factor

A highway section has been observed to be highly congested during peak hours. Being a 'traffic Engineer, you need to analyse the existing characteristics of traffic stream.. Traffic data related to the highway section  revealed that additional vehicles, equivalent to 28% of the capacity of this highway   section, could enter into the traffic stream, from 9.00 AM to 10.00 AM (peak hour), before the maximum theoretical vehicular flow is reached. Vehicle count during the given peak period is 2500 with ea mean speed of 65; mph. Determine following during  the given peak time period:

a.  Peak hour traffic

Answer is (1-0.28=0.72) 

But how? Kindly elaborate the answer