Box 1:
Rule2 blocks ports 50-60, which includes port 53, the DNS port. Internet users can reach to the Web server, since it uses port 80.
Box 2:
If Rule2 is removed internet users can reach the DNS server as well.
Note: Rules are processed in priority order, with lower numbers processed before higher numbers, because lower numbers have higher priority. Once traffic matches a rule, processing stops. As a result, any rules that exist with lower priorities (higher numbers) that have the same attributes as rules with higher priorities are not processed.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-network/security-overview
