Here are the steps and explanations for ensuring that subnet4-3 can accommodate 507 hosts:

To determine the subnet size that can accommodate 507 hosts, you need to use the formula: number of hosts = 2^(32 - n) - 2, where n is the number of bits in the subnet mask1. You need to find the value of n that satisfies this equation for 507 hosts.

To solve this equation, you can use trial and error or a binary search method. For example, you can start with n = 24, which is the default subnet mask for Class C networks. Then, plug in the value of n into the formula and see if it is too big or too small for 507 hosts.

If you try n = 24, you get number of hosts = 2^(32 - 24) - 2 = 254, which is too small. You need to increase the value of n to get a larger number of hosts.

If you try n = 25, you get number of hosts = 2^(32 - 25) - 2 = 510, which is just enough to accommodate 507 hosts. You can stop here or try a smaller value of n to see if it still works.

If you try n = 26, you get number of hosts = 2^(32 - 26) - 2 = 254, which is too small again. You need to decrease the value of n to get a larger number of hosts.

Therefore, the smallest value of n that can accommodate 507 hosts is n = 25. This means that the subnet mask for subnet4-3 should be /25 or 255.255.255.128 in dot-decimal notation1.

To change the subnet mask for subnet4-3, you need to go to the Azure portal and select your virtual network. Then select Subnets under Settings and select subnet4-3 from the list2.

On the Edit subnet page, under Address range (CIDR block), change the value from /24 to /25. Then select Save2.