Subnet Mask : - 255.255.240.0
$\underbrace{11111111 . 11111111 . 1111 }_{net\ id }\underbrace{0000.00000000 }_{host \ id}$
It is a class B network.For a class B network, the upper 16 bits form the network address and lower 16 bits are subnet and host fields.
of the lower 16 bits most significant 4 bits are 1111.This leaves 12 bits for the host number.So,4096(212) host address exists.
First and Last address are special so the maximum number of address
=4096-2=4094