One of the answers provided by a tutor states

"Subnet address of the second subnet: 180.100.8.0

The first subnet has all subnet bits 0 with subnet ID in decimal as 0. The second subnet has subnet number 1 with subnet ID in binary 00001. The network ID remains the same and the host ID is 0 for the subnet ID. So, the subnet ID of the second subnet is:

10110100.01100100.00001000.00000000

This can be shown in decimal as: 180.100.8.0 "

however if only 21 bits can't be changed wouldn't it be 180.100.4.0 instead of 8? because the bit that represents 8 is the 21st bit