Solve the system by the method of your choice.
12x2 + y2 = 156
xy = 12

The answer to the problem is as follows:

Look at the pieces. BC = BD
 
This might suggest that x = 16, but keep thinking.

68 < 78, to x < 16, but not a whole lot less.

The upper triangle exists, so x shoudl be nowhere near zero.

There might be a ratio that would help.
 
68/78 = 0.87, so x might be around 87% of 16, or 14 ish.

So letter A would be the answer.

I hope my answer has come to your help. God bless and have a nice day ahead!