From the question we can understand that the ratio of concentrate to water is 1:3. ie 25% of concenrtate is mixed with 75% of water to create 100% juice.

Now the problem asks for how many 12 ounce cans are needed to make 200 6 ounce cans. 200 6oz cans is same as 100 12oz cans.
So the problem reduces to "how many 12 oz cans are needed to make 100 12 oz cans of orange juice?"

Now it is very obvious that for 100 0z we need 25oz concenrtate and 75 oz water.

Ht Helps
-V

Wow! Thank you Vittalgmat! I definitely understand it now, and where I went wrong.