a sum of money at simple interest amounts to rs . 815 in 3 years and to rs . 874 in 4 years . the sum is :
"s . i . for 1 year = rs . ( 874 - 815 ) = rs . 59 . s . i . for 3 years = rs . ( 59 x 3 ) = rs . 177 . principal = rs . ( 815 - 177 ) = rs . 638 . answer : option b"
subtract(815, divide(multiply(subtract(874, 815), 3), 4))