21/x-4=21/4 решите уравнение
21/х - 4 = 21/4 21/х = 21/4 + 4 21/х= 21/4 +16/4 21/х= 37/4 х= 21 : 37/4 х= 21 * 4/37 = 84/37 = 2 10/37