Roots of a Cubic Polynomial

The equation $\displaystyle x^3-6x^2+21x-26=0$ has one real root and two complex roots of the form $\displaystyle x_1=a+bi$ and $\displaystyle x_2=a-bi$ where $\displaystyle a,b$ are real numbers. Find a+b

I'm not sure where to begin. I don't understand how to solve these kinds of expressions. Sometimes can group terms and find a way to factor the polynomial so that the roots are obvious. I don't understand how his would work if some of the roots were complex numbers. Would the equation take the form:

$\displaystyle (x\pm(a+bi))(x\pm(a-bi))(x\pm c)=0$

?