$f(x,y,z)=1+2xy2-xyz$

Find $(2$ marks each$)$:

$($a$)f_x(x,y,z)(b)f_{yy}(x,y,z)$

$($c$)f_{yy}(1,2,3)$

$2.$ If the weekly cost, $C,($in dollars$)$ to manufacture $L$ laptops and $D$ desktops is

$C(L,D)=50L^2-25DL+20D^2$

What is the marginal cost of a laptop at a production level of $10$ laptops and $12$ desktops?