Figure the advertisement should show a bed (4-6)
I believe the answer is:
four-poster
'a bed' is the definition.
(four-poster is a kind of bed)
'figure the advertisement' is the subsidiary indication.
'figure' becomes 'four' (I've seen this before).
'the advertisement' becomes 'poster' (I've seen this before).
'four'+'poster'='fourposter'
'should show' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for four-poster that I've seen before include "Style of bed" , "Large bed" , "Imposing item of bedroom furniture" , "Canopied bed" , "Type of bed" .)