Task: Question Answering
Input (English): Problem: peter invests a sum of money and gets back an amount of $ 815 in 3 years . david invests an equal amount of money and gets an amount of $ 870 in 4 years . if both amounts were invested at the same rate ( simple interest ) what was the sum of money invested ? 
Options: a ) 670 , b ) 650 , c ) 698 , d ) 744 , e ) 700
Output (English): b