Hi DorenOn.
To score 85 or higher on the Quant section, you have to miss a maximum of 2 medium-level questions, and you may score 84 with 2 missed medium-level questions.
Alternatively, you can miss a maximum of 3 hard questions and score 85.
So, if you miss medium questions, you need to get 19/21 questions or 90.5% correct.
If you miss only hard questions, you may score 85 with 18/21 or 86% correct.
We can define medium questions as questions labeled 600 - 655 and 655 - 705 on GMAT Club.
We can define hard questions as questions labeled 705 and higher on GMAT Club.
Also, there may be some questions labeled 655 - 705 that could be considered hard.
In any case, you can see that, to achieve a Q85+ score, you should be getting at least around 90% of 605 - 655 and 655 - 705 level practice questions correct and 86% of questions rated 705 or higher correct.
So, to achieve your target score, you have to increase your practice accuracies.
Also, you can be even more certain that you'll score 85+ if you can achieve streaks of 20 or more correct in a row. To learn how to use the streaks method to achieve your target score, see this post.
How to Ace the GMAT Using the Streaks Method