\[6\frac{7^{\backslash 4}}{45} - 4\frac{7^{\backslash 9}}{20} = 6\frac{28}{180} - 4\frac{63}{180} =\]
\[= 5\frac{208}{180} - 4\frac{63}{180} = 1\frac{145}{180} = 1\frac{29}{36}\]