We know that the ratio of strawberries to raspberries in the drink is 6 to 12. This ratio is equal to 1 to 2.
This means that for each strawberry there are 2 raspberries.
Then, we can find the percentage by assuming we need 100 berries. This is the sum of the strawberries S and raspberries R. Then we can write:

From the ratio, we know that there are 2 raspberries for each strawberry. This means that the amount of raspberries R is double the amount of strawberries.
Then, we can write:

If we replace in the first equation, we get:

As 100 represents the total (100%), then we can conclude that the strawberries represent 33.33% and the rapsberries represent 66.66%.
Answer:
Raspberries: 66,66%
Strawberries: 33.33%