\(\dfrac{3}{8}+\dfrac{3}{4}=\dfrac{3+3\cdot2}{8}=\dfrac{9}{8}\)
\(\dfrac{3}{4}\cdot12=\dfrac{3\cdot12}{4}=\dfrac{36}{4}=9\)
\(\dfrac{1}{6}-\dfrac{1}{12}=\dfrac{2}{12}-\dfrac{1}{12}=\dfrac{1}{12}\)
\(\dfrac{13}{7}-\dfrac{9}{5}=\dfrac{13\cdot5-9\cdot7}{7\cdot5}=\dfrac{2}{35}\)
\(\dfrac{3}{8}:2=\dfrac{3}{8\cdot2}=\dfrac{3}{16}\)