The mean is simply the average of the total movies seen so..
the median is the middle number (or the average of the middle 2 numbers) so if we line up the numbers in order and cross them out from both ends we get 12 & 14 so we take the average of the 2
The reason why I don't agree with Priya is because 25 Inch side blocks are BIGGER than 15 inch side blocks. That means that it will take less amount of 25 inch side blocks to fill up the volume of the rectangular prism rather than 15 inch side blocks.
(I'm sorry, I don't know what was your previous question, so I can't answer that part. If you comment it below, I will do it!)
So we want to know what do we need to measure to determine the wavelength of the wave on the image. A wavelength is the distance between peaks of the wave. More generally, the distance on which the wave shape repeats. So on the image we need to measure X to determine the wavelength. So the correct answer is X.