If x, y and z are real numbers such that (x - 3)2 + (y - 4)2 + (z - 5)2 = 0, then (x + y + z) is equal to?

Answer: Option D

This is possible only when
$$\begin{array}{rl}& {\left(x-3\right)}^2=0\\ & x=3\\ & {\left(y-4\right)}^2=0\\ & y=4\\ & {\left(z-5\right)}^2=0\\ & z=5\\ & \text{Then, }\left(x+y+z\right)\\ & =3+4+5\\ & =12\end{array}$$