Let the price of 1 goat be rs x.
Then the price of 1 sheep is 2x rs.

the average price of 12 goats and 12 sheeps is rs 600

So  12x + 12(2x) = 600
       12x + 24x = 600
             36x = 600
               x = 
               x =  rs  

So the average price of a goat is  rs

And the average price of a sheep is 2 times  rs. which
is  rs.

Therefore 3 goats sell for 3 times  or 50 rs
Therefore 2 sheep sell for 2 times  or  rs.

 rs.

Edwin