Subject: mathqa
Question: peter invests a sum of money and gets back an amount of $ 810 in 3 years . david invests an equal amount of money and gets an amount of $ 854 in 4 years . if both amounts were invested at the same rate ( simple interest ) what was the sum of money invested ?
Option: 
A: 744
B: 670
C: 683
D: 698
Answer: C