input: Write a Python function named find_coordinates that receives a 2D list (as nested lists) along with an integer x. This function should locate all instances of x within the list and return the coordinates as a list of tuples where each tuple represents (row, column). The coordinates should first be sorted by rows in ascending order, and within each row, by columns in descending order.
  
  Examples:
  find_coordinates([
    [1,2,3,4,5,6],
    [1,2,3,4,1,6],
    [1,2,3,4,5,1]
  ], 1) == [(0, 0), (1, 4), (1, 0), (2, 5), (2, 0)]
  find_coordinates([], 1) == []
  find_coordinates([[], [1], [1, 2, 3]], 3) == [(2, 2)]
output: def find_coordinates(lst, x):
      coordinates = [(i, j) for i, row in enumerate(lst) for j, val in enumerate(row) if val == x]
      coordinates.sort(key=lambda coord: (coord[0], -coord[1]))
      return coordinates