Answer
$x+y+z=\frac{11}{6}$
Work Step by Step
The general form of the equation of the plane is:
$a(x-x_0)+b(y-y_0)+c(z-z_0)=0$
or, $ax+by+cz=ax_0+by_0+cz_0$
Plugging in the given values, we get
$1x+1y+1z=1(1)+1(1/2)+1(1/3)$
After simplification, we get
$x+y+z=\frac{11}{6}$
