Task: Question Answering
Input (English): Problem: peter invested a certain sum of money in a simple interest bond whose value grew to $ 400 at the end of 4 years and to $ 500 at the end of another 2 years . what was the rate of interest in which he invested his sum ? 
Options: a ) 12 % , b ) 12.5 % , c ) 67 % , d ) 25 % , e ) 33 %
Output (English): d