The expression $\displaystyle\frac{{{x}+{5}}}{{{25}{x}}}\div\frac{{{{x}}^{{2}}+{12}{x}+{35}}}{{{35}{x}}}\usepackage{cmbright}\Huge\$ simplifies to: $\displaystyle\frac{{7}}{{{5}{x}+?}}\usepackage{cmbright}\Huge\$

The missing number is _____.