Explanation:
7 = 7×1 = 7×1000/1000 = 7000/1000
7000/1000 + 81/1000 = 7081/1000
this can't be further simplified, as the only factors of 1000 are
2 and 5 and then multiples of them.
neither of them can be a factor of 7081 (which is clearly neither an even number nor a multiple of 5).