The correct answer is C.
OBJ-1.4: To answer this question, you must be able to perform a basic subnetting calculation. First, you need to determine the number of IP addresses that will be needed. In this scenario, you have 57 clients that will each need an IP address, but you also need one IP address for the network and a second IP for the broadcast. This means you need 59 IP addresses total. IP addresses are assigned in multiples of 2 (1, 2, 4, 8, 16, 32, 64, 128, 256). Since we need 59 IP addresses, we need to round up to a block of 64. To symbolize a CIDR block with 64 IP addresses, we would use /26, which is 2^6 = 64.