I got this by dividing the whole 2/3 of licorice with 10 pieces to get 2/30 (2/3 divided by 10, which eventually becomes 2/3 multiplied by 1/10 to equal 2/30). Then, you simplify it to 1/15. So, each piece would be 1/15 of a yard long.
D. because there is one measurement or rate over one unit. In this case, 1 gallon. The one at the denominator is important in figuring out which one is a unit rate. Hope this helps.