Solve for each intercept. You can do this by substituting $0$ for two of the variables and solving for the remaining variable.

$2x - 3(0) + 4(0) = 12$  
                              $2x = 12$  
                                 $x = 6$
$(6, 0, 0)$

$2(0) - 3y + 4(0) = 12$  
                          $-3y = 12$  
                               $y = -4$
$(0, -4, 0)$

$2(0) - 3(0) + 4z = 12$  
                              $4z = 12$  
                                 $z = 3$
$(0, 0, 3)$

Now that you know the $x-$, $y-$, and $z$-intercepts, plot the points, connect them, and shade them to look like a plane.

Solve for the intercepts like you did in part (a).
Note that there is no $z$-intercept.