Answer: Third option is correct.
Step-by-step explanation:
Since we have given that
there are two similar televisions at a local electronics store,
Dimension of generic television set is
12 inches by 24 inches
We need to calculate the dimensions of brand name television ,
Since it is also given that the generic television was two third of the size of the brand name, i.e.

Now,

So, length of brand name television becomes

Breadth of brand name television becomes

So, Dimension of brand name television is
18 inches by 36 inches
So, Third option is correct.