(1/4) * х + (1/3) * х = (1/4 + 1/3) * х = ((1 * 3 +1 * 4) / (4 * 3)) * х = (7/12) * х .

(8/15) * у – (2/5) * у =(8/15 – 2/5) * у = ((1 * 8 – 2 * 3) / 15) * у = (2/15) * у.

(3/4) * м – (1/6) * м = (3/4 – 1/6) * м = ((3 * 3 – 1 * 2) / 12) * м = (7/12) * м.