a.appscript

function countFilesInFolder() {
  var c=1;
  var size = 0;
  var folderName = "Packs3";
  var folders = DriveApp.searchFolders('sharedWithMe and title contains "'+folderName+'"');
  var folder = folders.next().getFiles();
  while (folder.hasNext()){
    var file = folder.next();
    c+=1;
    size +=file.getSize();
  }
  Logger.log(c);
  Logger.log(size);
  return;
}