Marginal Productivity Consider the Cobb$-$Douglas production function $f(x,y)=400x^{0\mathrm{.}6}{y}^{0\mathrm{.}4}.$ When $x=700$ and $y=900,$ find the following. $($Round your answers to two decimal places.$)$

$($a$)$ the marginal productivity of labor, $\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{x}}$

$($b$)$ the marginal productivity of capital, $\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{y}}$