一、解方程。
3.5 + 4x = 27.7
5x÷3 = 3.2
x - 3.7 + 6.4 = 12
x÷0.63 + 2 = 12
4x - 0.5x = 1.75
5×2.1 + 2x = 57.3
7x - 4.2×4 = 29.4
2.8x + 2.5 = 6.42
x - (4.2 + 2.5) = 1.34
35x + 13x = 9.6
(x - 2)÷4 = 7.5
8x + 3×2.4 = 15.6
2.5x + 3x = 11
5x - 0.2x = 0.96
0.5x - 11.2 = 19.6

$x = 6.05$
$x = 1.92$
$x = 9.3$
$x = 6.3$
$x = 0.5$
$x = 23.4$
$x = 6.6$
$x = 1.4$
$x = 8.04$
$x = 0.2$
$x = 32$
$x = 1.05$
$x = 2$
$x = 0.2$
$x = 61.6$

二、计算下面各题，怎样简便就怎样计算。
12.39 - 4.68 + 2.68
5.4×58 + 4.2×54
35.72 - 4.9 - (5.72 + 5.1)
1.25×0.32×2.5 + 2.5
31.7 - 0.5×0.7 - 1.65
(7.34 - 4.17)×500 + 1725
3.5×0.26 + 1.25÷5
(37.5 - 4.8)÷5×0.15
6.4×5.8 + 4.6×5.8 - 5.8
17.6 - 7.8×0.34÷6.8
0.85×9.9 + 0.085
4.5×[(5.52 - 5.48)÷0.01]
5.4÷(0.3 + 6×0.2)
11.93 + 2.7 + 2.07 + 7.3
3.6÷[0.36÷(0.12 + 0.6)]

10.39 540 20
3.5 29.7 3310
1.16 0.981 58
17.21 8.5 18
3.6 24 7.2