Task: Question Answering
Input (English): Problem: a walks at 30 kmph and 30 hours after his start , b cycles after him at 50 kmph . how far from the start does b catch up with a ? 
Options: a ) 1200 km , b ) 1500 km , c ) 2000 km , d ) 2250 km , e ) 3600 km
Output (English): d