Bootstraping Web Page

It could sound a little weird but i need some help, the web page have to have a row which have to contain three sections, the first section must have an offset of 1 column, and the space between the sections must be 10px up to this part everything goes well using bootstrap.

Now a second row will have 2 equal sections, its edges have to be align with the edges of the previous row, the first section will have an offset of 1 column and the space between sections must be 10px.

My problem is in the second row how can I create this two sections of the same width with a 10px distance between them and also that its edges aligned to the edges of the previos row.

I let you a picture of the problem.

The code of my first row is:

<div class="barra row">
        <div class="col-md-3 col-md-offset-1 col-sm-3 col-xs-3 col-xs-offset-1 colum4"></div>
        <div class="col-md-3 col-sm-3 col-xs-3 leftMargin colum4" id="a"></div>
        <div class="col-md-3 col-sm-3 col-xs-3 leftMargin colum4" id="b"></div> 
</div>

What will be the second row code??