I assume you meant that Cara used 1/6 of the bucket and Carl used 2/3. If that is the case, then there is 2 oz left in the bucket.
Below is the Math to support the answer:
1/6 x 12/1 = 12/6 = 2 oz This is the amount Cara used.
2/3 x 12/1 = 24/3 = 8 oz This is the amount Carl used.
Together they used a total of 10 oz (8 + 2 = 10)
and so there are 2 oz remaining in the bucket of clay (12-10 = 2).