Maintain Aspect Ratio mixin (https://css-tricks.com/snippets/sass/maintain-aspect-ratio-mixin/)

_aspect-ratio.scss

@mixin aspect-ratio($width, $height) {
position: relative;
  &:before {
    display: block;
    content: "";
    width: 100%;
    padding-top: ($height / $width) * 100%;
  }
  > .content {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
  }
}

aspect-ratio-demo.html

<div class="sixteen-nine">
    <div class="content">
        insert content here
        this will maintain a 16:9 aspect ratio
    </div>
</div>

aspect-ratio-demo.scss

.sixteen-nine {
    @include aspect-ratio(16, 9);
}

and with images how???