From the diagram we can see that the lines used for the de-mux select lines are S1,S0 connected to $A_{13}$ and $A_{12}$
demux send the input to the selected output line
input to demux input is 1 when $A_{15}=0,A_{14}=0,A_{11}=1,A_{10}=0,,$
$A_0$ to $A_9$ used for address connected common to all memory chips
RAM #1
$S_{1}=0,S_{0}=0$ that is $A_{13},A_{12}$ both 0
so input $A_{15}A_{14}$ $A_{13}A_{12}$ $A_{11}-A_{8}$ $A_{7}-A_{4}$ $A_{3}-A_{0}$
can be in range of
$00$ $00$ $1000$ $0000$ $0000$ to $00$ $00$ $1011$ $1111$ $1111$ that is $0800_{16}-0BFF_{16}$
RAM #2
$S_{1}=0,S_{0}=1$ that is $A_{13}=0,A_{12}=1$
so input $A_{15}A_{14}$ $A_{13}A_{12}$ $A_{11}-A_{8}$ $A_{7}-A_{4}$ $A_{3}-A_{0}$
can be in range of
$00$ $01$ $1000$ $0000$ $0000$ to $00$ $01$ $1011$ $1111$ $1111$ that is $1800_{16}-1BFF_{16}$
RAM #3
$S_{1}=1,S_{0}=0$ that is $A_{13}=1,A_{12}=0$
so input $A_{15}A_{14}$ $A_{13}A_{12}$ $A_{11}-A_{8}$ $A_{7}-A_{4}$ $A_{3}-A_{0}$
can be in range of
$00$ $10$ $1000$ $0000$ $0000$ to $00$ $10$ $1011$ $1111$ $1111$ that is $2800_{16}-2BFF_{16}$
RAM #4
$S_{1}=1,S_{0}=1$ that is $A_{13}=1,A_{12}=1$
so input $A_{15}A_{14}$ $A_{13}A_{12}$ $A_{11}-A_{8}$ $A_{7}-A_{4}$ $A_{3}-A_{0}$
can be in range of
$00$ $11$ $1000$ $0000$ $0000$ to $00$ $11$ $1011$ $1111$ $1111$ that is $3800_{16}-3BFF_{16}$
