please answer this

As the network administrator for a growing ISP, you want to make efficient use of your network addresses. One of the networks addresses IANA assigned to you is a Class C network of 194.15.78.0. You have decided to use the addresses in this class C network to satisfy the IP address requirements of 24 corporate customers who need between 20 and 24 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.[5 marks]