I have a bottle of 88% lactic acid solution. I want to make a 10%-12% 1 oz or 2 oz. solution from it. How much H2O (teaspoons) do I need to put in it, to make it a 10% or 12% solution?
Thank you.
You’re new here, so just in case you aren’t aware of it, asking others to do your homework is frowned upon.
Why not at least show us your attempt at an answer and then I’m sure someone will be along to give you some pointers. But, again, no one’s gonna do your homework for you. 
I’ve never seen a homework assignment that has requirements that are this imprecise. And in imperial units?
Anyways, the main thing you need to remember is your conversion tables between those measurements. The rest is pretty simple. (Multiplication is your friend.)
And remember 88% = 0.88; 12% = 0.12, etc.
I think it’s interesting that 88% is about 8/9, and the final solution is to be a 10 - 12% solution which looks a lot like 1/9. So, I think the teacher was being pretty straight up about things.
We also have to know whether the percentages given are by weight or volume, or if the question is implicitly assuming that the two are the same (generally a bad assumption, for solutions).
V1C1 = V2C2.
I can’t count how many times that equation has saved my butt.
An 88% solution will almost certainly be by weight (w/w). This solution is quite syrupy, and has a specific gravity of 1.20; the usual volumetric techniques and approximations are invalid.