You don't know how many chocolates are in the boxes, so that's x. Always look at "and" and think + something. You know how many extra chocolates there are so you don't need to put the x. Remember, and=plus. Remember the equation is Mx+b.
The two expressions together is 3x+5=4x+8. Move the 4x to the other side with 3x+5 and make it negative. Same for eight. Hopefully that helps.
