一、解方程。
$6x - 72 = 6$ $7x - 2.5x = 13.5$ $7 + 4.2x = 11.2$
$7.5\div2.5 + x = 10.2$ $15x - 5\times4 = 85$ $5.6x - 3.9x = 54.4$
$x\div(18 + 7)=6$ $7.5x + x = 31.45$ $6\times0.4 + 2x = 9.6$
$3.2 + 5.4 - 2.3x = 2.85$ $5.7x\div4 = 34.2$ $x\div(20 - 10.5)=41.8$
$4.7 + 3x = 7.4$ $9x - 3.2 = 5.8$ $4 + 3.6x = 12.1$

$x = 13$
$x = 3$
$x = 1$
$x = 7.2$
$x = 7$
$x = 32$
$x = 150$
$x = 3.7$
$x = 3.6$
$x = 2.5$
$x = 24$
$x = 397.1$
$x = 0.9$
$x = 1$
$x = 2.25$

二、计算下面各题，怎样简便就怎样计算。
$9.1\div2.6 - 2.88$ $4.7 + 3.91\div(32 - 29.7)$ $(3.6 + 8.4)\times(4.68\div1.8)$
$2.1\times4.3 + 5.7\times2.1$ $3.8\times5.25 + 14.5\times0.2$ $480\div[(890 - 218)\div56]$
$(32 - 2.5\times8)\div15$ $205-(3.05 + 7.1)\times16$ $3.375\times0.97 + 0.97\times6.625$
$6.54 + 2.4 + 3.46 + 0.6$ $5000 - 105\times34 + 1825$ $37\times1.5 + 64\times1.5 - 1.5$
$125 - 100\div(2.07 - 1.27)$ $15.2\times0.25 + 12.8\div4$ $20.4\div[(7.2 - 0.4)\times25]$

0.62 6.4 31.2
21 22.85 40
0.8 42.6 9.7
13 3255 150
0 7 0.12