How can I make an image full width inside a paragraph which is 70% (text) [closed]

Solved, JS with jQuery width(), removeAttr() to avoid wordpress inline width and height. Also negative margins.

 var anchoArticulo = $('article.single-post').width();
    $('article.single-post div.single-post img.ancho_completo')
    .removeAttr('width height')
    .css('margin-left' , -(winWidth - anchoArticulo)/2)
    .css('width' , winWidth);

Class ancho_completo is added in dashboard to the image.