Fixed query typo

Author: sourabhbagrecha

docs/50-aggregation/4-group.mdx

@@ -93,7 +93,6 @@ db.books.aggregate([
 
 ## 👐 Example 3: Find the total number of pages published every year.
 
-
 ### **MongoDB query**
 
 ```js
@@ -130,7 +129,6 @@ GROUP BY year;
 
 ## 👐 Challenge
 
-
 ### 👐 1. Find the average book rating of all books
 
 <details>
@@ -157,7 +155,7 @@ GROUP BY year;
   - $group with $sort 
   - $sortByCount
   <Tabs groupId="aggregations">
-    <TabItem value="atlas" label="$group with $sum + $sort">
+    <TabItem value="$group with $sum + $sort" label="$group with $sum + $sort">
     ```js
     db.reviews.aggregate([
       {
@@ -175,7 +173,7 @@ GROUP BY year;
     ```
     </TabItem>
 
-    <TabItem value="mongodb-shell" label="$sortByCount">
+    <TabItem value="sortByCount" label="$sortByCount">
     ```js
     db.reviews.aggregate([
       {

docs/50-aggregation/7-merge.mdx

@@ -1,3 +1,6 @@
+import Tabs from "@theme/Tabs";
+import TabItem from "@theme/TabItem";
+
 # 🦸 $merge
 
 In MongoDB, the **$merge** stage allows you to **write the results of an aggregation pipeline into a new or existing collection**. This is similar to the concept of "INSERT INTO ... SELECT" or "MERGE INTO" in SQL databases.
@@ -89,18 +92,45 @@ ON DUPLICATE KEY UPDATE totalBooks = VALUES(totalBooks);
 
 <details>
   <summary>Answer</summary>
-  ```js
-    db.books.aggregate([
-      { $unwind: "$authors" },
-      { $group: { _id: "$authors.name", totalBooks: { $sum: 1 } } },
+  <div>
+  There are 2 ways to solve this- 
+  - through `books` collection
+  - through `authors` collection
+  <Tabs groupId="aggregations">
+    <TabItem value="books" label="through 'books' collection">
+    ```js
+      db.books.aggregate([
+        { $unwind: "$authors" },
+        { $group: { _id: "$authors.name", totalBooks: { $sum: 1 } } },
+        {
+          $merge: {
+            into: "author_stats",
+            on: "_id",
+            whenMatched: "merge",
+            whenNotMatched: "insert",
+          },
+        },
+      ]);
+    ```
+    </TabItem>
+
+    <TabItem value="authors" label="through 'authors' collection">
+    ```js
+    db.authors.aggregate([
+      { $unwind: "$books" },
+      { $group: { _id: "$name", totalBooks: { $sum: 1 } } },
       {
         $merge: {
           into: "author_stats",
           on: "_id",
           whenMatched: "merge",
-          whenNotMatched: "insert",
-        },
-      },
+          whenNotMatched: "insert"
+        }
+      }
     ]);
     ```
+    </TabItem>
+
+  </Tabs>
+  </div>
 </details>