Sovis, I have created a linear equation question with code description at Solving EQUATIONS with FORMULAS question (teacher/teacher).
In addition we have updated to Moodle 3.2 with the BOOST theme, so we can confirm FORMULAS is working fine at M3.2 and that the new theme is superb.
BTW, I have used your "chk" trick in order no to get indefined solutions, thanks.