Wow I'd love to go to that store of yours! :P Anyways if you were asking for the new discounted price I solved this equation: 12*0.8 and got $9.60. But if it was asking for <em>how </em> <em>much </em>was discounted, I would do 12*0.2 and $2.40.
This is just substitution. so 3(2(3)-4(1/2)+3(-2/3)= 3(6-2-2)= 3(2) = 6. Basically you plug in the values they gave you for the variables and then just solve one step at a time