Final answer:
The index variable for the element at the last row and last column in array x is [1][3].
Step-by-step explanation:
The index variable for the element at the last row and last column in array x can be determined using the equation: index = number_of_rows - 1 for the row and index = number_of_columns - 1 for the column.
In this case, the array x has 2 rows and 4 columns, so the index variable for the last row is 2 - 1 = 1 and the index variable for the last column is 4 - 1 = 3.
Therefore, the element at the last row and last column in array x has the index [1][3].