How many usable host are there per subnet if you have the address of 192.168.10.0 with a subnet mask of 255.255.255.240?

4 is the number of host bits, not the usable hosts.

8 would be the number of usable hosts for a /29 subnet (2^3 - 2).

16 is the total number of addresses in the subnet, including the network and broadcast addresses, not the usable hosts.

A subnet mask of 255.255.255.240 corresponds to a /28 CIDR notation, indicating 28 network bits. This leaves 32 - 28 = 4 bits for host addresses. The total number of addresses in the subnet is 2^4 = 16, and by subtracting two addresses for the network address and the broadcast address, we get 16 - 2 = 14 usable host addresses.