Orly uses 2 cups of raisins for every 8 cups of trail mix she makes. how many cups of trail mix will she make is she uses 12 cups of raisins?

We will be working with ratios.
2 cups of raisins: 8 cups of trail mix
The question is asking for the amount of trail mix with 12 cups of raisins.
2 cups of raisins: 8 cups of trail mix
12 cups of raisins: x cups of trail mix
Whatever you do to one side of the ratio, you have to do to the other. Look at the cup of raisins, you multiplied it by 6 (12÷2) to get your new batch. So, you have to do it with the trail mix.
8×6=48=x
She will have 48 cups of trail mix with 12 cups of raisins.

You have a 2:8 ratio, or 1:4.  Since you have 12 cups of raisins, you're going to get the answer 48.