answer : option C
[tex](4r^{-2}st^4)^2(r^{-4}st^6)^{-2}[/tex]
Multiply the exponent -2 inside the parenthesis
[tex](4^2r^{-4}s^2t^8)(r^{8}s^{-2}t^{-12})[/tex]
When we multiply same terms we add the exponents
[tex](4^2r^{-4+8}s^{2-2}t^{8-12})[/tex]
[tex](4^2r^{4}s^{0}t^{-4})[/tex]
Now make the exponent positive
[tex]\frac{16r^4}{t^4}[/tex]
