The scaled size of the thumbnails is 16 pixels per inch of painting
The given parameters are:
The space between adjacent images is 40 inches.
Given that there are two spaces, the remaining space is:
Remaining = 800 - 2 * 40
Remaining = 720
Given that there are three samples of image, the width of each image is:
Image = 720/3
Divide
Image = 240 pixels
The scaled size is then calculated using:
Scale = Image scale width/actual width
This gives
Scale = 240/15
Evaluate
Scale = 16
Hence, the scaled size of the thumbnails is 16 pixels per inch of painting
Read more about dilation at:
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