864 is decomposed first, because 864 =12 *12 * 6 =12 * 2 *12 * 3 = 24 * 36.

Because the difference between length and width is12,24,36, which meets the question.

So the answer is 24, 36.

The second method. Consider that when the length is equal to the width (that is, assuming the length is less than 12), it becomes a square. There must be an area number that is square (because all data have no decimals and fractions), and the reduced area is a multiple of 12.

Considering that a number of 864 minus a multiple of 12 becomes a square number, it is easy to get 864- 12*24=576.

And 24 is just the width (also the assumed length), so the width is 24 and the easy length is 36.