\[7\frac{13}{36} - 3\frac{25}{54} = 6\frac{49^{\backslash 3}}{36} - 3\frac{25^{\backslash 2}}{54} =\]
\[= 6\ \frac{147}{108} - 3\frac{50}{108} = 3\frac{97}{108}\]