feat: add sum with image reference problem

ENDPOINTS-EXAMPLE.md

@@ -66,3 +66,31 @@ curl -X POST "http://127.0.0.1:8000/math/grade_1/compose_and_decompose_numbers"
     "seed": 1
   }'
 ```
+
+### Sum with image reference
+
+```bash
+curl -X POST "http://127.0.0.1:8000/math/grade_1/sum_with_image_reference" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "first_quantity": 5,
+    "second_quantity": 4,
+    "first_description": "flores rojas",
+    "second_description": "flores blancas",
+    "common_object": "flores",
+    "first_picture": {
+      "id": "red-flower",
+      "name": "Red flower",
+      "image_path": "/images/red-flower.png"
+    },
+    "second_picture": {
+      "id": "white-flower",
+      "name": "White flower",
+      "image_path": "/images/white-flower.png"
+    },
+    "option_count": 3,
+    "min_option_quantity": 1,
+    "max_option_quantity": 20,
+    "seed": 1
+  }'
+```