Incorrect. Distribute the subtraction sign to both terms in the subtrahend.

$\displaystyle{\left({4}+{5}{i}\right)}-{\left({6}-{i}\right)}={4}+{5}{i}-{6}+{i}\usepackage{cmbright}\Huge\$

Rearrange the terms to put like terms together, and then combine like terms. The correct answer is $\displaystyle{6}{i}\usepackage{cmbright}\Huge\$ .