The ratio of the trout with tags that are caught and the total trout with tags is first calculated.
r = 12 trout / 180 trout = 1/15
Then, we divide the number of trouts caught without tag by the value obtained above.
N = (48 - 12) / (1/15) = 540
Then, we add the number obtained above and 180.
T = 540 + 180 = 720
ANSWER: 720
The square of a binomial is written like
In your case, you have 
, which implies 
So, we want to write
But our left hand side is
If we add 26 to both sides, we have
You were right, its the second choice CA=CB+BA
Hmmm wait let me try to do it
So
2/6 of 318=106
so 106-1/2 or 106/2=53
So he has 53 boxes left
