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These are percentages you use in Photoshop after you've scanned. There are some scan applications that can apply a curve adjustment in the scan process, a form of automation. But, I'd do it in PS. Now, there is the possibility, based on the original art/photo, final percentages fall within these guidelines ( although highly unlikely ). The numbers themselves tell you how much dot gain the printer is anticipating on-press. If you scan a full color image and open it in PS, you can use the Eyedropper and the Info palette to show you the percentages in the image. You can manually sample the highlight ( lightest area ), qtr. tones, mids, and shadow ( darkest area ). If it is a CMYK image, you'll be able to read the percentages for each process color. Not all of the process colors will need to be adjusted. Often times the Yellow may not need adjusting. Here's a quick overview of their numbers:

Highlight = 3-5%; refers to the lightest area in the image. The printer is trying to avoid "Hotspots"; a percentage of 0%. In my opinion, their press has aged considerably and may be using film to plate where their platemaker cannot image a dot smaller than 3-5%; instead a 3-5% yields a 1-3% highlight.

Quarter / mid tones = 21-46%; these numbers tell how well the press can hold midtones. They are anticipating a 4-6% dot gain in the midtones.

Shadows = 85%; indicates the darkest area of the image. Typically, in a process color image, you'd be interested in Cyan and Black percentages, and the number itself tell you they are anticipating a 15% dot gain in the shadows. This means that your 85% Black will actually end-up at around 93-100%. This is probably the most critical number out of the four. Why? Because if you did not adjust, either in the scan application or Photoshop, and you supplied the printer with an image at 1% Highlts; 25% qtr; 95% shadows; then after dot gain, the final printed image will be a flood at 400+% ink coverage, which means the paper will offset ( be wet stacked and end up sticking and transferring to the other side of the next sheet ), the ink will crack, puddle, and split, and in order to try to control the problem on press, the pressperson will have to cut the fountains back considerably with the final image ending up faded or color casted. And, because they cannot hold a dot of 1-3%, your image highlights will become hotspots.

It also appears they are anticipating a coated sheet ( paper ). By limiting the percentages to around 300-340%, they will be able to control and makeready the press run. Each printer is different, but you should keep your shadows at 85-87%; newer presses may be able to accept 90-93% shadows, but that would depend on what type of paper is being used. Very tricky stuff, but the prepress and press people are letting you know their acceptable parameters using a certain press / paper combination.