Find all the first and second order partial derivatives $of$

$f(x,y)=-6sin(2x+y)+9cos(x-y).$

$A.\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{x}}=f_x=$

$B.\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{y}}=f_y=$

$C.\frac{de{l}^{2}f}{del{x}^2}=f_{}=$

$D.\frac{de{l}^{2}f}{del{y}^2}=f_{yy}=$

$E.\frac{de{l}^{2}f}{\text{d}\text{e}\text{l}\text{x}\text{d}\text{e}\text{l}\text{y}}=f_{yx}=$

$F.\frac{de{l}^{2}f}{\text{d}\text{e}\text{l}\text{y}\text{d}\text{e}\text{l}\text{x}}=f_{xy}=$