$4.($a$)$ Convert the following Hex numbers to binary and add them. Express your final answer in HEX $2$A$7$E $+45$CB $($b$)$ Write down the $2$s complement of the following binary number $10110000($c$)$ Convert the following numbers to binary and evaluate using the $2$s complement method. Leave your answer in binary form. $68145($d$)$ Write down the BCD form of decimal $936.$