add Q4

Q4-Scalability/calculations.md

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+# Container Capacity Calculation
+
+## Given
+
+- Expected Traffic = 15,000 requests/second
+- One container capacity = 500 requests/second
+- Required headroom = 30%
+
+---
+
+## Step 1
+
+Number of containers without headroom
+
+15000 / 500 = 30 Containers
+
+---
+
+## Step 2
+
+Adding 30% reserve capacity
+
+30 × 1.30 = 39 Containers
+
+---
+
+## Final Result
+
+The application should run **39 containers** to safely handle the expected traffic while maintaining additional capacity for sudden traffic spikes and infrastructure failures.