a)
[tex](4- \sqrt{5} ) - ( \sqrt{5} - 4) = 4 - \sqrt{5} - \sqrt{5} + 4 = \boxed{8 - 2 \sqrt{5} }[/tex]
[tex] \boxed{ \boxed{Odp.B}}[/tex]
b)
[tex](4 - \sqrt{5} ) \times ( \sqrt{5} - 4) = 4 \sqrt{5} - 16 - \sqrt{25} + 4 \sqrt{5} = 2 \times 4 \sqrt{5} - 16 - 5 = \boxed{ 8 \sqrt{5} - 21}[/tex]
[tex] \boxed{ \boxed{Odp.D}}[/tex]
