(х + 3) / 7 = (2х - 1) / 5,
5 * (х + 3) = 7 * (2х - 1),
5х + 15 = 14х - 7,
5х - 14х = -7 - 15,
-9х = -22,
х = -22 : (-9),
х = 22/9,
х = 2 4/9,
проверка:
(22/9 + 3) / 7 = (2*22/9 - 1) / 5,
(22/9 + 27/9) / 7 = (44/9 - 9/9) / 5,
49/9 / 7 = 35/9 / 5,
49/9 * 1/7 = 35/9 * 1/5,
7/9 = 7/9