1.
-28 + 12 * 7 = -28 + 84 = 56,
2.
2/7 + 3/8 : 7/32 = 2/7 + 3/8 * 32/7 = 2/7 + 12/7 = 14/7 = 2,
3.
-7,1 + 7,68 : 1,2 = -7,1 + 6,4 = -0,7,
4.
х - 2*(х + 3) = х - 2х - 6 = -х - 6,
при х = 7: -7 - 6 = -13,
5.
9/22 - 4/9 : (3 - 1 8/15) + 8/11 = 5/6,
1) 3 - 1 8/15 = 2 15/15 - 1 8/15 = 1 7/15,
2) 4/9 : 1 7/15 = 4/9 : 22/15 = 4/9 * 15/22 = 10/33,
3) 9/22 - 10/33 + 8/11 = 27/66 - 20/66 + 48/66 = 55/66 = 5/6