Does anyone know how to fix this error. I've tried typing it in many different ways.

public static double getGrade $($int grade$)\{$

if $($grade $<mtext></mtext><mi>\backslash </mi>$varnothing $||$ grade $>10\backslash$varnothing$)\{$

throw new IllegalArguementException$()$;

e$15-$getGrade $1$ of $1$ problem

cannot find symbol: class Illega$|$ArguementException

$\}$

double x $=\mathrm{.}8$;

if $($grade $<mtext></mtext><mn>6</mn><mi></mi><mi>)</mi>$

return $\backslash$varnothing$.\backslash$varnothing;

else if $($grade

return $\mathrm{.}7$;

else if $($grade

for $($int i $=63$; i $$ grade; i $++)$

x $+=\mathrm{.}1$;

return x;

$\}$

else

return $4\mathrm{.}0$;

$\}$

$19$

$20$

$21$

$22$