What is the address of the element 14 in matrix D?

Since you have not provided the matrix, I cannot tell you the exact address of the element.

However, what I can do is to tell you how to identify the address of a certain element.

We will refer to the element by the symbol "A".

This symbol is usually followed by by 2 subscripts:

The first subscript usually indicates the row

The second subscript usually indicates the column

For example:

element A12 is located in the first row, the second column

element A43 is located in the fourth row, the third column

Apply this to the matrix you have to get the address of the desired element