Find the subnet ID from the IP address 10.75.20.3/24

(A) 10.75.5.0
(B) 10.75.0.0
(C) 10.75.20.0
(D) 10.0.0.0

10.75.20.0 is the correct answer.

IP address = 10.75.20.3/24
Subnet mask = 255.255.255.0
The subnet mask can be found from the prefix length /24.
To find the subnet ID follow the steps for each of the four octets.
Step 1) If the mask octet = 255, copy the decimal IP address.
Step 2) If the mask octet = 0, write a decimal 0.
The subnet ID for 10.75.20.3/24 is 10.75.20.0