Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="l-example">
  <div class="l-example__a">A<br/>&nbsp;</div>
  <div class="l-example__b">B</div>
  <div class="l-example__c">C</div>
</div>

SassMeister-input.scss

// ----
// Sass (v3.3.5)
// Compass (v1.0.0.alpha.18)
// Zen Grids (v)
// ----

@import "zen";

$zen-column-count: 12;
$zen-gutter-width: 30px;
$zen-auto-include-item-base: false;

.l-example {
  @include zen-grid-container;
}
.l-example__a, .l-example__b, .l-example__c {
  @include zen-grid-item-base;
}
.l-example__a {
  background: #fcc;
  @include zen-grid-item(8, 1);
}
.l-example__b {
  background: #cfc;
  @include zen-grid-item(4, 1, right);
}
.l-example__c {
  background: #ccf;
  @include zen-clear(right);
  @include zen-grid-item(4, 1, right);
}

SassMeister-output.css

.l-example:before, .l-example:after {
  content: "";
  display: table;
}
.l-example:after {
  clear: both;
}

.l-example__a, .l-example__b, .l-example__c {
  padding-left: 15px;
  padding-right: 15px;
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -ms-box-sizing: border-box;
  box-sizing: border-box;
  word-wrap: break-word;
}

.l-example__a {
  background: #fcc;
  float: left;
  width: 66.66667%;
  margin-left: 0%;
  margin-right: -66.66667%;
}

.l-example__b {
  background: #cfc;
  float: right;
  width: 33.33333%;
  margin-right: 0%;
  margin-left: -33.33333%;
}

.l-example__c {
  background: #ccf;
  clear: right;
  float: right;
  width: 33.33333%;
  margin-right: 0%;
  margin-left: -33.33333%;
}

SassMeister-rendered.html

<div class="l-example">
  <div class="l-example__a">A<br/>&nbsp;</div>
  <div class="l-example__b">B</div>
  <div class="l-example__c">C</div>
</div>