How do I modify a datagrid from diffrent ViewModels

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C#

WPF

MVVM

I have a View with multiple UserControls. Each UserControl has its one ViewModel. The ViewModels inheritances from a baseViewModel, which implements the INotifyPropertyChanged stuff.
One of the viewmodel contains a datagrid and another has a textbox and an apply button. Independently everything is working fine. But I would like to apply the entered number from the textbox in the list from the other ViewModel.

Does anyone have a dummy friendly explanation to achieve this?

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<img src="http://image-upload.de/thumb/ZAscqq/5285303a83.jpg" alt="image-upload.de" border="0">

Which way should I use? No1 Direct comunication ViewModel1 <-> ViewMode2 or No2 ViewModel1<->Model<->ViewModel2