I just did it the easy way and multiplied .85 (value range) by .2, and .15 is air
that came out to .32 and we needed .33 so I increased air by 2% and got 33.6%

you can do a formula something like (1-air%)*equity + air% = equity we need

so in our example it would be (1-A)*.2 + A = .33
.2 - .2A + A = .33
.8A = .13
A = 16.25% which is more accurate