(3\14+5\21X):3\7=3 1\4
(3/14 + 5/21х) : 3/7 = 3 1/4 3/14 + 5/21х = 13/4 * 3/7 3/14 + 5/21х = 39/28 5/21х = 39/28 - 6/28 = 33/28 х = 33/28 : 5/21 х = 33/28 * 21/5 = (33*3)/(4*5) х = 99/20 х = 4 целых 19/20