$\frac{12}{17}$ : 4 = $\frac{12}{17}\times\frac{1}{4}$ = $\frac{12}{68}$
$12 : \frac{6}{13}=12\times \frac{13}{6}=\frac{12\times 13}{6}=\frac{156}{6}=26$
$9 \times \frac{5}{3}\times \frac{4}{15}=\frac{9\times 5\times 4}{1\times 3\times 15}=\frac{180}{45}=4$