now discussing the question: well logically, you must find for the ratio 13:15:18 angles 45 45 90 degs for the plane cutting the cube, in that case this is the most effective coz tan(45) is 1 in equation ax+by+cz+d=1/3*(234+270+324), picture ^^^ , this question was: my better graphical solution was 1:1:1 🙃 to have clean 45 45 90 degs graph ^^^

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