a) $$|-3 - (-7)| = |-3 + 7| = |4| = 4$$
б) $$|-4,2 - 2,3| = |-6,5| = 6,5$$
в) $$|\frac{1}{6} - (-\frac{2}{3})| = |\frac{1}{6} + \frac{4}{6}| = |\frac{5}{6}| = \frac{5}{6}$$
г) $$|1\frac{2}{7} - (-2\frac{5}{7})| = |\frac{9}{7} + \frac{19}{7}| = |\frac{28}{7}| = |4| = 4$$