\[5\frac{3}{7} + \left( - 2\frac{1}{4} \right) - \left( - 3\frac{3}{28} \right) =\]
\[= 5\frac{12}{28} - 2\frac{7}{28} + 3\frac{3}{28} =\]
\[= 8\frac{15}{28} - 2\frac{7}{28} = 6\frac{8}{28} = 6\frac{2}{7}\]