Refactor is_international and get_fees methods in Package struct

exercises/07_structs/structs3.rs

@@ -7,7 +7,7 @@
 // Execute `rustlings hint structs3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
+// NOTE 結構體關聯函式與方法
 
 #[derive(Debug)]
 struct Package {
@@ -31,12 +31,14 @@ impl Package {
         }
     }
 
-    fn is_international(&self) -> ??? {
+    fn is_international(&self) -> bool {
         // Something goes here...
+        if self.sender_country == self.recipient_country { false } else { true }
     }
 
-    fn get_fees(&self, cents_per_gram: u32) -> ??? {
+    fn get_fees(&self, cents_per_gram: u32) -> u32 {
         // Something goes here...
+        self.weight_in_grams * cents_per_gram
     }
 }