Calculus: Early Transcendentals 8th Edition

$x+y+z=\frac{11}{6}$
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 $x+y+z=\frac{11}{6}$