if x / y = 2 / 7 , then ( x + y ) / ( x - y ) = ?
"any x and y satisfying x / y = 2 / 7 should give the same value for ( x + y ) / ( x - y ) . say x = 2 and y = 7 , then ( x + y ) / ( x - y ) = ( 2 + 7 ) / ( 2 - 7 ) = - 9 / 5 . answer : d ."
divide(add(2, 7), subtract(2, 7))