postMetrics
  .map(post => post.views > 100)
  .reduce((acc, post) => acc + post.likes + post.comments, 0) / postMetrics.length;

postMetrics
  .filter(post => post.views > 100)
  .reduce((acc, post) => acc + post.likes + post.comments, 0) / 
  postMetrics.filter(post => post.views > 100).length;

postMetrics

  .filter(post => post.views > 100)

  .map(post => post.likes + post.comments)

  .reduce((acc, total) => acc + total) / postMetrics.length;

postMetrics
  .reduce((acc, post) => {
    return post.views > 100 ? acc + post.likes + post.comments : acc;
  }, 0) / postMetrics.filter(post => post.views > 100).length;