get length

main.dart

void main() {
  List<Map<String, dynamic>> data = [
    {"title": "A"},
    {
      "title": "B",
      "options": [
        {"name": "Joko Widodo"},
        {"name": "Maruf Amin"},
        {"name": "Tidak tahu"},
        {"name": "Tidak Menjawab"}
      ]
    },
    {
      "title": "C",
      "options": [
        {"name": "Joko Widodo"},
        {"name": "Maruf Amin"},
        {"name": "Tidak tahu"},
        {"name": "Tidak Menjawab"}
      ]
    },
    {
      "title": "D",
      "options": [
        {"name": "sangat puas"},
        {"name": "puas"},
        {"name": "kecewa"},
        {"name": "sangat kecewa"}
      ]
    }
  ];

  var asem =
      data.where((e) => e["title"] == 'B').toList().first['options'].length;
  print(asem.toString());
}