complement to represent negative numbers. $($If overflow occurs, enter OVERFLOW.$)$

$($a$)(-15)+(-6)$

$2\text{'}$s complement

$1\text{'}$s complement

$($b$)(-15)+(-8)$

$2\text{'}$s complement

$1\text{'}$s complement

$($c$)(-13)+(-6)$

$2\text{'}$s complement

$1\text{'}$s complement

$($d$)6+7$

$2\text{'}$s complement

$1\text{'}$s complement

$($e$)(-6)+(-5)$

$2\text{'}$s complement

$1\text{'}$s complement