How to add numeric value as seconds to a datetime field and report data in new column

I need to convert the ElapsedTime field into hours/minutes/seconds and add that to the creationtime field and have the results reported into a new column that I'll call EndTime. Here is the query I have to gather the data:

select ElapsedTime, ChannelUsed, documents.creationtime from historytrx (nolock) inner join history on historytrx.handle = history.handle inner join documents on history.owner = documents.handle inner join DocFiles on documents.docfiledba = docfiles.handle where creationtime > '2015-02-02 20:00:00.000' and creationtime < '2015-02-02 20:01:00.000'  and RemoteServer = 'DMG4120-01668' and ElapsedTime != '0'

Here is the current output:

ElapsedTime   ChannelUsed    creationtime
1042          1              2015-02-02 20:00:03.000
27            35             2015-02-02 20:00:05.000
57            50             2015-02-02 20:00:05.000

Here is my desired output:

ElapsedTime   ChannelUsed    creationtime             EndTime
1042          1              2015-02-02 20:00:03.000  2015-02-02 20:17:39.000
27            35             2015-02-02 20:00:05.000  2015-02-02 20:00:32.000
57            50             2015-02-02 20:00:05.000  2015-02-02 20:01:03.000

Thanks to everyone in advance for any assistance.