#11 Outside Gray

[El Santo]

When I was panic-buying tins of every Colourcoats shade I could imagine wanting in response to the news that Sovereign Hobbies was going out of business, I accidentally bought more #7 Neutral Navy Gray than I needed. That being so, I thought I'd try converting the spare tin to #11 Outside Gray, the post-1945 US Navy shade intermediate between Navy Gray and the reformulated neutral Ocean Gray. Presumably the way to do that is to just add a little white (and obviously I'll be using Colourcoats white to keep all the binders and whatnot consistent), but the quantity is the problem-- especially since these paints are, at least for the moment, a non-renewable resource.

Given 14 milliliters of neutral gray paint that dries to 7% light reflectance, how much white is needed to lighten it to 11%?