2,1/2у это 2целых 1/2
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2 целых 1/2 = 2,5 в десятичных дробях--------------------------------------------------------2,3у + 31 + 2,5у = 672,3у + 2,5у = 67 - 314,8у = 36у = 36 : 4,8у = 7,5Проверка: 2,3 * 7,5 + 31 + 2,5 * 7,5 = 67                   17,25 + 31 + 18,75 = 67                    67 = 67