ЯсноПонятно24

<Window x:Class="CalculatorInterface.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Calculator" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        
        <TextBox Grid.Row="0" Text="Previous Operations" HorizontalAlignment="Stretch" VerticalAlignment="Center" Margin="10"/>
        
        <TextBox Grid.Row="1" Text="Current Number" HorizontalAlignment="Stretch" VerticalAlignment="Center" Margin="10"/>
    </Grid>
</Window>