Task: Question Answering
Input (English): Problem: mike drives his new corvette from san francisco to las vegas , a journey of 640 miles . he drives the first half of the trip at an average rate of 80 miles per hour , but has to slow down for the second half of his journey . if the second half of the trip takes him 200 percent longer than the first half , what is his average rate z in miles per hour for the entire trip ? 
Options: a ) 26.7 , b ) z = 30.0 , c ) z = 40.0 , d ) z = 53.3 , e ) 60.0
Output (English): c