The number of elements to be added is calculated in this way;
Total Number of Elements to be added = No. of pairs of matrix * ( no. of elements in each matrix)
for 3 matrix; it would come to ; total number of operations required =
(n*n) * 2 ( as there are 2 add operations , m1 + m2 + m3) ~= O(2*(n^2))
For large number of n; it would be O(N^2)
O(n^2), addition count will be 2n^2.