As the network administrator for a growing ISP, you want to make efficient use of your network addresses. One of the network addresses IANA assigned to you is a Class C network of 197.15.10.0. You have decided to use the addresses in this Class C network to satisfy the IP address requirements of 16 corporate customers who need 20 addresses each. Without using a subnet calculator, calculate a subnet mask that meets their needs. List the subnet mask and the first four subnetwork addresses the mask will create