Решите уравнение; 5/7 умножить (21/20-х) + 16/21 разделить на 8/7 = одна целая 1/4

5/7 * (21/20 - х) + 16/21 : 8/7 = 1 1/4,

5/7 * (21/20 - х) + 16/21 * 7/8 = (1 * 4 + 1) / 4,

5/7 * (21/20 - х) + 2/3 = 5/4,

5/7 * (21/20 - х) = 5/4 - 2/3,

5/7 * (21/20 - х) = (5 * 3) / 12 - (2 * 4) / 12,

5/7 * (21/20 - х) = 15/12 - 8/12,

5/7 * (21/20 - х) = (15 - 8) / 12,

5/7 * (21/20 - х) = 7/12,

21/20 - х = 7/12 : 5/7,

21/20 - х = 7/12 * 7/5,

21/20 - х = 49/60,

х = 21/20 - 49/60,

х = (21 * 3) / 60 - 49/60,

х = 63/60 - 49/60,

х = (63 - 49) / 60,

х = 14/60 = 7/30,

Ответ: х = 7/30.