An example of using a basic breakpoint mixin...

example-rule.scss

body.single-peopleandplaces {
  .wrap .photo {
    height: ( $photoheight / 2 );
    width: 100%;
    @include bp(medium) {
      height: ( $photoheight * .75 );
      width: ( 100% / 2 );
    }
    @include bp(large) {
      height: $photoheight;
      width: ( 100% / 3 );
    }
  }
}