If a man travels f miles an hour for t hours and r kilometers an hour for s hours, what is his average rate in kilometers per hour for the entire distance traveled?	Choose the correct option.
A) ft + rs kms/hr	B) (ft + rs)/2 kms/hr	C) t/f + s/r kms/hr	D) (ft + rs)/(t + s) kms/hr	E) (ft + rs)/(t - s) kms/hr
Average Speed = Total (ft + rs)/(t + s) kms/hristance /Total Time Taken   Total (ft + rs)/(t + s) kms/hristance travelled in t hours = ft   Total (ft + rs)/(t + s) kms/hristance travelled in s hours = rs   Total Time taken = t+s   Therefore , Average Speed = (ft+ts)/(t+s) kms/hr   Answer (ft + rs)/(t + s) kms/hr
<result>D</result>
If a man travels f miles an hour for t hours and r kilometers an hour for s hours, what is his average rate in kilometers per hour for the entire distance traveled?