(3 3/7 - 1 1/4) * 2,8 = 6 1/10   (или 6,1),

1) 3 3/7 - 1 1/4 = (3 - 1) + (3/7 - 1/4) = 2 + (12/28 - 7/28) = 2 + 5/28 = 2 5/28,

2) 2 5/28 * 2,8 = 61/28 * 28/10 = 61/10 = 6 1/10   (или 6,1),

0,6*(х + 7) = 0,5*(х - 3) + 6,8,

0,6х + 4,2 = 0,5х - 1,5 + 6,8,

0,6х - 0,5х = 6,8 - 1,5 - 4,2,

0,1х = 1,1,

х = 11