Consider the following Scheme function fun:

$($DEFINE $($fun k x$)$

$($COND

$(($NULL$?$ x$)\text{'}())$

$(=$ k $($CAR x$))$ x$)$

$($ELSE $($fun k $($CDR x$)))$

In each of the following cases, give the value of the expression and explain how it was derived.

$($a$)($fun $8\text{'}())$

$($b$)($fun $8(4892))$