add ListView Summs Liter Price per Year

lib/data/models/tank_model.dart

@@ -10,6 +10,7 @@ class AppWriteTankModel {
   String? imageFileName;
   String? imageFileUrl;
   int? mnIndexCount;
+  String? szSummePreis;
 
   AppWriteTankModel({
     required this.documentId,
@@ -22,7 +23,9 @@ class AppWriteTankModel {
     this.imageFileId,
     this.imageFileName,
     this.imageFileUrl,
-  });
+  }):szSummePreis = (double.tryParse(liters) != null && double.tryParse(pricePerLiter) != null)
+        ? (double.parse(liters) * double.parse(pricePerLiter)).toStringAsFixed(2)
+        : null;
 
   factory AppWriteTankModel.fromMap(Map<String, dynamic> map) {
     return AppWriteTankModel(