If the production function is

$F(K,L)=(0\mathrm{.}8L^6+0\mathrm{.}2K^6{)}^{\frac{1}{6}}$

What is the marginal product of labour $(L)$ when $K=L=2?$

$($A$)5\mathrm{.}6$

$($B$)5\mathrm{.}8$

$($C$)6\mathrm{.}2$

$($D$)6\mathrm{.}4$

$($E$)$ None of the above.