Question

If they are right triangles

Answer 1

Yes they are right triangles 

Answer 2

You can use Pythagreos theorem to determine it!
Pythagreos theorem is a^2 + b^2 = c^2
1) 4^2 + 4^2 = 6^2
   16    +  16  = 36
         32       = 36 (So this is not a right-angled triangle )
2) 16^2 + 12^2 = 20^2
      256 + 144  = 400
       400          = 400 (Sp this is a right-ngled triangle)