Dissolution of firm- plz help

While solving a dissolution problem I came across a particular adjustment which goes like:

Fixed Assets realised at a loss of 100% on Net collection.The value of Fixed assets is 40000 as per the B/S.

The entry given is

bank a/c(fixed assets)..................................Dr.  15000

to Realisation a/c.................................................................15000

Plz help how to go about solving this.How did this figure of 15000 come?