$1\mathrm{.}17$ Perform subtraction on the given unsigned numbers using the $10\text{'}$s complement of the subtrahend. Where the result should be negative, find its $10\text{'}$s complement and affix a minus sign. Verify your answers.

$($a$)4,637-2,579$

$($b$)125-1,800$

$($c$)2,043-4,361$

$($d$)1,631-745$

$1\mathrm{.}20$ Convert decimal $+49$ and $+29$ to binary, using the signed$-2\text{'}$s$-$complement representation and enough digits to accommodate the numbers. Then perform the binary equivalent of $(+29)+(-49),(-29)+(+49),$ and $(-29)+(-49).$ Convert the answers back to decimal and verify that they are correct.

$1\mathrm{.}22$ Convert decimal $6,514$ to both BCD and ASCII codes. For ASCII, an even parity bit is to be appended at the left.