To understand the percentage difference between two numbers, we first need to know what percentage means. Percentage is a way of expressing a number as a fraction of 100. For example, 50% means 50 out of 100 or 0.5 as a decimal.

Now, let's look at the problem at hand. We are given two numbers, 135 and 150, and we need to find the percentage difference between them. To do this, we first need to find the absolute difference between the two numbers, which is simply the difference between them without considering whether it is positive or negative. In this case, the absolute difference between 135 and 150 is 15.

Next, we need to find the relative difference between the two numbers, which is the absolute difference expressed as a percentage of the average of the two numbers. The average of 135 and 150 is (135+150)/2 = 142.5. So, the relative difference between 135 and 150 is:

(relative difference) = (absolute difference) / (average of the two numbers) x 100%
(relative difference) = 15 / 142.5 x 100%
(relative difference) = 10.53%

Therefore, the percentage difference between 135 and 150 is 10.53%. This means that 150 is 10.53% greater than 135.