If x, y, z are the three factors of a³ - 7a - 6, then value of x + y + z will be?

$$\eqalign{ & {a^3} - 7a - 6 \cr & \left( {a + 1} \right)\left( {{a^2} - a - 6} \right) \cr & \left( {a + 1} \right)\left( {a + 2} \right)\left( {a - 3} \right) \cr & {\text{Now}},{\text{Sum of factors}} \cr & \left( {a + 1} \right) + a + 2 + a - 3 = 3a \cr} $$