4/15x+2,8=6,3-3/20x

4/15х + 2,8 = 6,3 - 3/20х;4/15х + 3/20х = 6,3 - 2,8;16/60х + 9/60х = 3,5;5/12х =3,5;х = 35/10 ÷ 5/12х = 35/10 × 12/5х = (7 × 6)/5х = 84/10х = 8,4Ответ: 8,4