Given equation is [3/x] + [4/x] = 5
when x is negative, the value of [3/x] + [4/x] can never be equal to 5 when x is positive, there are 3 possibilities

This is not possible simultaneously,
So, it has no solution.
From (ii), [3/x] = 1, then 1 ≤ 3/x < 2

This is not possible simultaneously,
So, it has no solution.
From (iii), we get,

Thus, a = 1, b = 4, c = 3
Hence, the value of a + b + c + abc + 30
= 1 + 4 + 3 + 12 + 30 = 50.