If x + y = z, then the expression x3 + y3 - z3 + 3xyz will be equal to?

Answer: Option A

$$\begin{array}{rl}& x+y=z\\ & x+y-z=0\\ & \text{If }a+b+c=0\\ & \text{then }{a}^3+b^3+c^3-3abc=0\\ & \Rightarrow x^3+y^3-z^3=-3xyz\\ & \therefore x^3+y^3-z^3+3xyz=0\\ & \Rightarrow 3xyz-3xyz=0\end{array}$$