General

I have the calculations somewhere. Hang on.

It costs roughly 55 clean slates per to pass one slot, give or take a bit. So approx 550 clean slates for 10 slot. Don't ask where I got that from, but that's assuming you have no bonus modifiers on your scroll success rates, like clean failure or diligence.

If you want, you can use (gasp) MATHS to solve this, through the use of a geometric progression. I will upload a spreadsheet for you later if I can.

Could cost 10m, could cost 40b, all depends on how lucky you are.

The only thing you can do to really know is to find theoretical price. 10% slates, so 1/10 slates will pass in theory. So ~300m per slot failed. Then knowing the scrolls are 15%, theoretically 1/7 scrolls will pass. Using that, count backwards from 10 and find out how many scrolls of each kind you would need.

@Harbors and how much wud dat be? thanks for ur helpful response though