20 bits are Network and subnet bits
so subnet mask is 11111111.11111111.11110000.00000000
since in subnet mask network and subnet bits are represented by 1's and Host bits are represented by 0's
IP address given 172 .16.40.0
10101100.00010000.00101000.00000000 (IP)
and 11111111. 11111111. 11110000. 00000000 (subnet mask)
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10101100.00010000.00100000.00000000 ----------> 172.16.32.0
therefore Answer is Option C
