P(x) is of degree 5,therefore it must have 5 roots. Since P(x) has real coefficients, the remaining root must be 1-2i according to the Complex Conjugates Theorem.
Now, we can write P(x) as below:
P(x) = (x - 7)^3*Q(x)
Q(x) is of degree 2 with the roots 1 + 2i and 1 - 2i because P(x) is of degree 5.
Q(x) = x^2 - (sum of the roots)x + product of the roots
= x^2 - (1-2i+(1+2i))x + ((1-2i)(1+2i))
= x^2 -2x + 5
P(x) = (x - 7)3(x2 - 2x + 5)