First of all, I'm not the best person to give out any advice regarding QR since I got a 17 myself

.
However, this is the way I see it...
Doing well on the QR section of the DAT has very little to do with your knowledge of mathematics; it's more about time management. I've taken many math classes throughout my college career and I never earned anything lower than B+. However, I can only do math, when I'm given enough time to think. That's why I struggled with the QR section of the DAT, where time is scarce.
So, what is my time management advice?
Don't waste more than a minute on any question. If you come across a word question that will take you just 30 seconds to read it and 20 seconds to think about how you'd go about solving it, then you need to move on. Just pick an answer (so you won't leave anything blank), mark it, and move on. Like you said, you're good at solving for X
😉, so try to answer the questions that you think you can answer correctly first. If you have time at the end, go back and focus on the marked questions.
Keep in mind that there are 40 math questions, so you can miss 6-7 questions and still end up with score in the 19's.
Finally, remember that QR is the least significant individual score. In other words, many students will do poorly in this section, which is why it wouldn't affect your application significantly, as long as you get a 17+.
However, by no means, does this mean you should ignore this section and not study for it. Like I said, try to see which types of questions your more comfortable answering, when you're practicing. This way you'll know which questions to answer first during your real exam.