= 6 + = a + = a + . Since "b" and "c" are positive integers with b < c, you can conclude that < 1. Hence, a = 6. But for "b" and "c" you have INFINITELY MANY answers (b,c) = (3,7), (6,14), (9,21) . . . and so on . . . Therefore, IT IS NOT POSSIBLE to evaluate the value of abc by an UNIQUE way. Your problem is posed INCORRECTLY.