diff --git a/webapp/controller/TankController.class.php b/webapp/controller/TankController.class.php
index 4ebfea4..505a6ad 100644
--- a/webapp/controller/TankController.class.php
+++ b/webapp/controller/TankController.class.php
@@ -447,7 +447,7 @@ class TankController{
             return;
         }
         $fragment_num = $t['cost'] * ceil($row['tank_level'] / 5) + $t['cost_int'];
-        $coin_num = $c['gold_cost'] * ceil($row['tank_level'] / 5) + $c['gold_cost_int'];
+        $coin_num = $t['gold_cost'] * ceil($row['tank_level'] / 5) + $t['gold_cost_int'];
         if ($free == 1) {
             $coin_num = 0;
             $fragment_num = 0;