Пошаговое объяснение:
21/20 × (12/ (6x+5)) -1/4 = 2/3
21/5 × (3/ (6x+5)) -1/4 =2/3
63/(5(6x+5)) -1/4 =2/3
63/(5 (6x+5))=2/3 + 1/4
63/(5 (6x+5))= 8/12 + 3/12
64/(5 (6x+5))=11/12
756=55 (6x+5)
756=330x+275
-330x=275-756
-330x=-481
330x=481
x=481/330
x= 1 151/330