Task: Question Answering
Input (English): Problem: circular gears l and r start to rotate at the same time at the same rate . gear l makes 10 complete revolutions per minute and gear r makes 40 revolutions per minute . how many seconds after the gears start to rotate will gear r have made exactly 9 more revolutions than gear l ? 
Options: a ) a ) 6 , b ) b ) 8 , c ) c ) 10 , d ) d ) 18 , e ) e ) 15
Output (English): d