If you are talking about the rowSums method that you need to write for Routine7B, then within the method you should "instantiate" a 1D array (use the new operator.....int sums = new int[......]) with the number of elements determined by the number of rows in the 2D array. You don't turn the 2D array into a 1D array, but create a 2nd array that is 1D.
Then, loop through the 2D array accumulating the sum of a row then store that sum into the corresponding element in the 1D array. Sum up row 0 of the 2D array and store the sum as element zero in the 1D array. Sum up row 1 of the 2D array and store the sum as element one in the 1D array, etc. Be sure that each time you begin to sum a new row, the accumulating sum has been reset to zero.