Chapter 5 - Linear Functions - 5-2 Direct Variation - Practice and Problem-Solving Exercises - Page 304: 20

$y=-18.667x; -224$

We know direct variation has the equation y=kx. Thus, we plug in the points and solve for k: $ y=kx \\\\ 9\frac{1}{3}=-.5k \\\\ k=-18.667$ We substitute k back in to get the equation: $y=-18.667x$ We now plug in x=12: $y=(-18.667)(12)=-224$