Let n be that unknown number of grandchildren. Then the number of cookies C = 4n +2, according to the first part of the condition. At the same time, C = 5n - 2, from the other part of the condition. It gives you an equation 4n + 2 = 5n -2, which gives you the solution n = 4. Answer. The number of grandchildren is 4. The number of cookies is 18.