Correct. Change the subtraction to adding the opposite: $\displaystyle{\left({7}{x}+{5}\right)}+{\left(-{3}{x}-{2}\right)}\usepackage{cmbright}\Huge\$

Regroup to match like terms: $\displaystyle{\left({7}{x}+-{3}{x}\right)}+{\left({5}+-{2}\right)}\usepackage{cmbright}\Huge\$

Combine like terms: $\displaystyle{4}{x}+{3}\usepackage{cmbright}\Huge\$

The missing coefficient is 4.