It's just basic maths. The cube root of 27 is 27**(1/3). If you really want a function, try

print wop(  8, 3 ); #2
print wop( 27, 3 ); #3

sub wop {
    my ( $base, $root ) = @_;
    return $base ** (1/$root)
}
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update: s/If/If you/