When Megh was small, his preprimary teacher was teaching counting of shapes.
She was teaching about this type of shapes and counting the number of triangles in them.For, example, the following shape has eight triangles
Imagine an \(n\times n\) grid made up of such boxes and count the number of triangles inside it. For example following is a \(4\times 4 \) grid
But when the teacher saw Megh scribbling in his notebook, she asked him to tell her the number of triangles in an \(4000\times 4000\) grid. To her surprise he answered the number of triangles \(x\) instantly.
Answer the digit sum of \(x\).