3. 计算。
(1) 直接写得数。
$\frac{3}{6} + \frac{2}{6} =$ $\frac{15}{17} - \frac{9}{17} =$ $1 - \frac{4}{9} =$ $\frac{5}{9} - \frac{3}{9} =$
$\frac{4}{15} + \frac{8}{15} =$ $\frac{15}{26} - \frac{7}{26} =$ $\frac{4}{15} + \frac{11}{15} =$ $1 - \frac{3}{13} =$
26.9 - 11.2 = 18.4 + 4 =
(2) 计算。
$\frac{4}{9} + \frac{2}{9} + \frac{6}{9}$ $\frac{7}{12} - \frac{5}{12} + \frac{11}{12}$ $0.25 × 39 + 0.25$ $0.125 × 72$
(3) 看图列方程并求解。

(1) $\frac{5}{6}$；$\frac{6}{17}$；$\frac{5}{9}$；$\frac{2}{9}$；$\frac{4}{5}$；$\frac{4}{13}$；1；$\frac{10}{13}$；15.7；22.4
(2) $\frac{4}{3}$；$\frac{13}{12}$；10；9
(3) $x=\frac{40}{3}$；$x=31$

(1) $\frac{3}{6}+\frac{2}{6}=\frac{5}{6}$；$\frac{15}{17}-\frac{9}{17}=\frac{6}{17}$；$1-\frac{4}{9}=\frac{5}{9}$；$\frac{5}{9}-\frac{3}{9}=\frac{2}{9}$；$\frac{4}{15}+\frac{8}{15}=\frac{12}{15}=\frac{4}{5}$；$\frac{15}{26}-\frac{7}{26}=\frac{8}{26}=\frac{4}{13}$；$\frac{4}{15}+\frac{11}{15}=1$；$1-\frac{3}{13}=\frac{10}{13}$；26.9-11.2=15.7；18.4+4=22.4
(2) $\frac{4}{9}+\frac{2}{9}+\frac{6}{9}=\frac{12}{9}=\frac{4}{3}$；$\frac{7}{12}-\frac{5}{12}+\frac{11}{12}=\frac{13}{12}$；0.25×39+0.25=0.25×(39+1)=0.25×40=10；0.125×72=0.125×8×9=1×9=9
(3) 左图：$3x - 5 = 35$，$3x=40$，$x=\frac{40}{3}$（原解析有误，修正后应为$3x - 5 = 35$，$3x=40$，$x=\frac{40}{3}$）；右图：$x + 2x = 93$，$3x=93$，$x=31$