Tính.

a) \(\frac{4}{7}\,\, + \,\,2\,\, = \,\,\frac{4}{7}\,\, + \,\,\frac{2}{1}\,\, = \,\,\frac{4}{7}\,\, + \,\,\frac{{14}}{7}\,\, = \,\,\frac{{18}}{7}\)

b) \(\frac{7}{9}\,\, - \,\,\frac{1}{3}\,\, = \,\,\frac{7}{9}\,\, - \,\,\frac{3}{9}\,\, = \,\,\frac{4}{9}\)

c) \(\frac{8}{{49}}\,\, \times \,\,\frac{{14}}{4}\,\, = \,\,\frac{{\cancel{4}\,\, \times \,\,2\,\, \times \,\,2\,\, \times \,\cancel{7}}}{{7\,\, \times \,\,\cancel{7}\,\, \times \,\,\cancel{4}}}\,\, = \,\,\frac{4}{7}\)

d) \(\frac{{18}}{{54}}\,\,:\,\,\frac{2}{9}\,\, = \,\,\frac{{18}}{{54}}\,\, \times \,\,\frac{9}{2}\,\, = \,\,\frac{{9\,\, \times \,\,\cancel{2}\,\, \times \,\,\cancel{9}}}{{6\,\, \times \,\,\cancel{9}\,\, \times \,\,\cancel{2}}}\,\, = \,\,\frac{9}{6}\,\, = \,\,\frac{3}{2}\)