a sum of money at simple interest amounts to $ 815 in 3 years and to $ 854 in 4 years . the sum is :
"b $ 698 s . i . for 1 year = $ ( 854 - 815 ) = $ 39 . s . i . for 3 years = $ ( 39 x 3 ) = $ 117 . principal = $ ( 815 - 117 ) = $ 698 ."
subtract(815, divide(multiply(subtract(854, 815), 3), 4))