$\frac{4 * 3}{27 * 8} = \frac{\overset{1}{\bcancel{4}} * \overset{1}{\bcancel{3}}}{\underset{9}{\bcancel{27}} * \underset{2}{\bcancel{8}}} = \frac{1}{18}$

$\frac{12 * 14}{35 * 15} = \frac{\overset{4}{\bcancel{12}} * \overset{2}{\bcancel{14}}}{\underset{5}{\bcancel{35}} * \underset{5}{\bcancel{15}}} = \frac{8}{25}$

$\frac{17 * 22}{55 * 34} = \frac{\overset{1}{\bcancel{17}} * \overset{2}{\bcancel{22}}}{\underset{5}{\bcancel{55}} * \underset{2}{\bcancel{34}}} = \frac{2}{10} = \frac{1}{5}$

$\frac{12 * 14}{35 * 15} = \frac{\overset{4}{\bcancel{12}} * \overset{2}{\bcancel{14}}}{\underset{5}{\bcancel{35}} * \underset{5}{\bcancel{15}}} = \frac{8}{25}$

$\frac{8 * 13 * 45}{15 * 24 * 39} = \frac{\overset{1}{\bcancel{8}} * \overset{1}{\bcancel{13}} * \overset{3}{\bcancel{45}}}{\underset{1}{\bcancel{15}} * \underset{3}{\bcancel{24}} * \underset{3}{\bcancel{39}}} = \frac{3}{9} = \frac{1}{3}$

$\frac{9 * 14 + 9 * 5}{18 * 38} = \frac{9 * (14 + 5)}{18 * 38} = \frac{9 * 19}{18 * 38} = \frac{\overset{1}{\bcancel{9}} * \overset{1}{\bcancel{19}}}{\underset{2}{\bcancel{18}} * \underset{2}{\bcancel{38}}} = \frac{1}{4}$

$\frac{15 * 21}{15 * 32 - 15 * 4} = \frac{15 * 21}{15 * (32 - 4)} = \frac{15 * 21}{15 * 28} = \frac{\overset{1}{\bcancel{15}} * \overset{3}{\bcancel{21}}}{\underset{1}{\bcancel{15}} * \underset{4}{\bcancel{28}}} = \frac{3}{4}$

$\frac{42 * 17 - 16 * 17}{51 * 7 + 51 * 6} = \frac{17 * (42 - 16)}{51 * (7 + 6)} = \frac{17 * 26}{51 * 13} = \frac{ \overset{1}{\bcancel{17}} * \overset{2}{\bcancel{26}}}{\underset{3}{\bcancel{51}} * \underset{1}{\bcancel{13}}} = \frac{2}{3}$