creating a 2 OS thumb drive

Code:

Microsoft Windows [Version 10.0.10240]
(c) 2015 Microsoft Corporation. All rights reserved.

C:\Windows\system32>Imagex /export "D:\Win7x64.wim" 1 "D:\x86\sources\install.wim" "Windows 7 Home Basic (x64)"

ImageX Tool for Windows
Copyright (C) Microsoft Corp. All rights reserved.
Version: 6.1.7600.16385

Exporting: [D:\Win7x64.wim, 1] ->
           [D:\x86\sources\install.wim]


[ 100% ] Exporting progress

Successfully exported image #1.


Total elapsed time: 1 min 8 sec





C:\Windows\system32>Imagex /export "D:\Win7x64.wim" 2 "D:\x86\sources\install.wim" "Windows 7 Home Premium (x64)"

ImageX Tool for Windows
Copyright (C) Microsoft Corp. All rights reserved.
Version: 6.1.7600.16385

Exporting: [D:\Win7x64.wim, 2] ->
           [D:\x86\sources\install.wim]


The specified image [2] was not found in [D:\Win7x64.wim].

C:\Windows\system32>

What went wrong? I don't know enough about what I am doing to fix this myself.