3. 计算下面各题，能简算的要简算。
$29+5×105+29$ $4\frac {3}{4}×0.8+\frac {2}{5}×6.25$
$(\frac {3}{8}-\frac {3}{8}×\frac {2}{5})÷\frac {1}{5}×5$ $[13-(4+5.6+0.7)]÷2.5$
$24×[(\frac {11}{8}-\frac {3}{4})×8]$ $25.2+\frac {5}{11}+4.8+\frac {6}{11}$
$9÷[1-(\frac {2}{5}+\frac {9}{20})]$ $3.5×\frac {4}{5}+5.5×80\% +0.8$

$29+5×105+29$
$=29+29+525$
$=58+525$
$=583$
$4\frac {3}{4}×0.8+\frac {2}{5}×6.25$
$=4.75×0.8+0.4×6.25$
$=3.8+2.5$
$=6.3$
$(\frac {3}{8}-\frac {3}{8}×\frac {2}{5})÷\frac {1}{5}×5$
$=\frac{3}{8}×(1-\frac{2}{5})×5×5$
$=\frac{3}{8}×\frac{3}{5}×25$
$=\frac{45}{8}$
$=5\frac{5}{8}$
$[13-(4+5.6+0.7)]÷2.5$
$=[13-(9.6+0.7)]÷2.5$
$=[13-10.3]÷2.5$
$=2.7÷2.5$
$=1.08$
$24×[(\frac {11}{8}-\frac {3}{4})×8]$
$=24×(\frac{11}{8}×8-\frac{3}{4}×8)$
$=24×(11-6)$
$=24×5$
$=120$
$25.2+\frac {5}{11}+4.8+\frac {6}{11}$
$=(25.2+4.8)+(\frac{5}{11}+\frac{6}{11})$
$=30+1$
$=31$
$9÷[1-(\frac {2}{5}+\frac {9}{20})]$
$=9÷[1-(\frac{8}{20}+\frac{9}{20})]$
$=9÷[1-\frac{17}{20}]$
$=9÷\frac{3}{20}$
$=9×\frac{20}{3}$
$=60$
$3.5×\frac {4}{5}+5.5×80\% +0.8$
$=3.5×0.8+5.5×0.8+0.8×1$
$=0.8×(3.5+5.5+1)$
$=0.8×10$
$=8$

4. 解方程。
$x-0.2x+4=28$ $\frac {9}{10}x-3\% x=5.22$ $\frac {5}{8}:x=\frac {3}{4}:0.8$
$x:21=96.2:7$ $8×(3.2-x)=4$ $1.5x+1.8=7.5$

解：$x-0.2x+4=28$
$0.8x+4=28$
$0.8x=28-4$
$0.8x=24$
$x=24÷0.8$
$x=30$
解：$\frac {9}{10}x-3\% x=5.22$
$0.9x-0.03x=5.22$
$0.87x=5.22$
$x=5.22÷0.87$
$x=6$
解：$\frac {5}{8}:x=\frac {3}{4}:0.8$
$\frac {3}{4}x=\frac {5}{8}×0.8$
$\frac {3}{4}x=0.5$
$x=0.5÷\frac {3}{4}$
$x=\frac {2}{3}$
解：$x:21=96.2:7$
$7x=21×96.2$
$7x=2020.2$
$x=2020.2÷7$
$x=288.6$
解：$8×(3.2-x)=4$
$3.2-x=4÷8$
$3.2-x=0.5$
$x=3.2-0.5$
$x=2.7$
解：$1.5x+1.8=7.5$
$1.5x=7.5-1.8$
$1.5x=5.7$
$x=5.7÷1.5$
$x=3.8$