The network IP address allocated to a network administrator is 172.31.0.0/20.

Which portion of the address is the network, which part is the host and which is the subnet mask?
n = network
s = subnet
h = host

nnnnnnnn.nnnnnnnn.nnnnssss.hhhhhhhh

would that bet correct?

This might help also:

ID	# Bits	Number Hosts	Usable Hosts	Netmask		Note
6	/6  	67108864	67108862	 252.0.0.0  	
7	/7 	33554432	33554430	254.0.0.0 	
8	/8 	16777216	16777214	255.0.0.0 	Class A Network 
9	/9 	8388608		8388606		255.128.0.0 	
10	/10 	4194304		4194302		255.192.0.0 	
11	/11 	2097152		2097150		255.224.0.0 	
12	/12 	1048576		1048574		255.240.0.0 	
13	/13 	524288		524286		255.248.0.0 	
14	/14 	262144		262142		255.252.0.0 	
15	/15 	131072		131070		255.254.0.0 	
16	/16 	65536		65534		255.255.0.0 	Class B Network 
17	/17 	32768		32766		255.255.128.0 	
18	/18 	16384		16382		255.255.192.0 	
19	/19 	8192		8190		255.255.224.0 	
20	/20 	4096		4094		255.255.240.0 	
21	/21 	2048		2046		255.255.248.0 	
22	/22 	1024		1022		255.255.252.0 	
23	/23 	512		510		255.255.254.0 	
24	/24 	256		254		255.255.255.0 	Class C Network 
25	/25 	128		126		255.255.255.128 	
26	/26 	64		62		255.255.255.192 	
28	/28	16		14		255.255.255.240	
27	/27	32		30		255.255.255.224	
29	/29 	8		6		255.255.255.248 	
30	/30 	4		2		255.255.255.252

Hi Bangor_boy.
The classful network is 172.31.0.0/16.The network you have is already subnetted and that's why it's 172.31.0.0/20 which will actually give you 16 subnets since 4 bits have been borrowed from the host bits of the /16 network. The 16 subnets are 172.31.0.0/20,172.31.16.0 up-to 172.31.240.0/20(note that it's a 16 jump). Each of the 16 subnets will have 4096 hosts.
So it should be nnnnnnnn.nnnnnnnn.sssshhhh.hhhhhhhh.
Hope this will help and also that you've learnt something more.

Would this be the same using subnet 0 as i've worked my way through a few questions and then seen i should be using this and im confused again

I.P subnet zero is usable by default on Cisco Routers and I believe also on Juniper routers. So you can use it.