Well, here's how...
Simply, when the degree of derivative you are looking for is higher than of the exponent in the given equation, the answer is always zero.
Nth Derivative of x^a + x^b + x^c + C
There is actually a proper solution to this but for simplicity, let's use the shortcut.
(And Neeluap is right about it that the value of the exponent will be multiplied to the constant of the term, then subtract 1 to the exponent,, it'll be the new term).
For simplicity, lets assume a value for N, a, b & c.
Let N=4, a=3, b=2, c=1
And so, 4th degree derivative of x^3 + x^2 + x + C
(From the given assumption, everything is fine since we've followed the condition).
(You may change the value of N, a, b & c to any number but let N be the highest on your assumption.)
1st Degree:
3x^(3-1) + 2x^(2-1) + 1 3x^2 + 2x
2nd Degree:
3(2)x^(2-1) + 2(1)x^(1-1) 6x +2
3rd Degree:
6(1)x^(1-1) 6
4th Degree:
6 is actually 6x^0
Therefore: 6(0)x^(0-1) is zero.
And so therefore; 5th, 6th, 7th, and so on and so forth Degree will result to zero.