there is same question on cheg, but I don$$t understand how he discussed XY based on C P G and why he only discussed what Y$1$Y$2$ refers to$.$ Shouldn$$t the $16-$digit number have $16$ bits Y$1$~Y$16$ in total $?$

$3.$We are performing a $16-$bit subtraction of Z $=$ X $-$ Y$,$ where X $=4587.$ Suppose some pieces of information are known on the $16-$bit fast adder$$s top$-$level CLA$74182$ circuit, as annotated by the red numbers $($P$1=1,$ C$2=0,$ C$3=1,$ P$4=0,$ and C$4=1).$

a$)$Please derive the possible values of Y$,$ you should provide evidence for your answer.

b$)$Please give the possible results of Z$,$ and whether overflow happens by using the signals in the circuit for your answer.r

why?:Since there is a carry$-$out, we conclude that Z will not overflow.we only getY$1$Y$2,$what is Y and Z actually??