Решение:

1) $$\frac{2}{15} - \frac{1}{6} = \frac{2*2}{15*2} - \frac{1*5}{6*5} = \frac{4}{30} - \frac{5}{30} = \frac{4-5}{30} = \frac{-1}{30} = -\frac{1}{30}$$

2) $$\frac{5}{7} + \frac{2}{3} = \frac{5*3}{7*3} + \frac{2*7}{3*7} = \frac{15}{21} + \frac{14}{21} = \frac{15+14}{21} = \frac{29}{21} = 1 \frac{8}{21}$$

3) $$\frac{3}{7} - \frac{2}{9} = \frac{3*9}{7*9} - \frac{2*7}{9*7} = \frac{27}{63} - \frac{14}{63} = \frac{27-14}{63} = \frac{13}{63}$$

4) $$\frac{46}{75} : \frac{23}{45} = \frac{46}{75} * \frac{45}{23} = \frac{46*45}{75*23} = \frac{2*23*3*15}{5*15*23} = \frac{2*3}{5} = \frac{6}{5} = 1 \frac{1}{5}$$

5) $$\frac{7}{16} * (\frac{12}{21}) = \frac{7*12}{16*21} = \frac{7*4*3}{4*4*7*3} = \frac{1}{4}$$

6) $$\frac{9}{16} * (-3) = -\frac{9*3}{16} = -\frac{27}{16} = -1 \frac{11}{16}$$

7) $$7 \frac{1}{11} : 2 \frac{7}{25} = \frac{7*11+1}{11} : \frac{2*25+7}{25} = \frac{78}{11} : \frac{57}{25} = \frac{78}{11} * \frac{25}{57} = \frac{78*25}{11*57} = \frac{2*39*25}{11*3*19} = \frac{2*13*25}{11*19} = \frac{650}{209} = 3 \frac{23}{209}$$