Task: Question Answering
Input (English): Problem: sari and ken climb up a mountain . at night , they camp together . on the day they are supposed to reach the summit , sari wakes up at 06 : 00 and starts climbing at a constant pace . ken starts climbing only at 08 : 00 , when sari is already 600 meters ahead of him . nevertheless , ken climbs at a constant pace of 500 meters per hour , and reaches the summit before sari . if sari is 50 meters behind ken when he reaches the summit , at what time did ken reach the summit ? 
Options: a ) 13 : 00 , b ) 11 : 15 , c ) 14 : 00 , d ) 15 : 00 , e ) 15 : 30
Output (English): b