To find the percentage difference between two numbers, we first need to calculate the absolute difference between them. In this case, the absolute difference between 111 and 129 is 18.

Next, we need to find the average of the two numbers. The average of 111 and 129 is (111+129)/2 = 120.

Now, we can calculate the percentage difference by dividing the absolute difference by the average and multiplying by 100. So, the percentage difference between 111 and 129 is (18/120) x 100 = 15%.

Therefore, the percentage difference between 111 and 129 is 15%. This means that 129 is 15% more than 111.