1) Pl_19 answer is right but in case you need a deeper understanding.
The key to make calculations with network blocks is to understand the idea of masks- the /something.
If you have a range of address x.y.z.t/27 and you binary AND the range with a number composed of 27 1's and (32-27) 0's you will get an address x.y.z.r which is named the Network address of your range.
Your /27 range is composed of 2^(32-27) = 32 addresses that go from x.y.z.r+0 to x.y.z.r+31. I will refer the addresses by the offset to the network address.
From this range you can't use the address '+0' which is the network address and the '+31' is named the broadcast address and is used if you want to send a packet to all the servers in your block.
All the other addresses in your block are considered local and to get them you don't need a default router.
2) The default gateway must be one of the addresses of the block (usually the first or the last usable one) and the provisioner must provide that information to you. This will be another address that you can't use.