It appears that you did not distribute the minus sign to the term $\displaystyle{6}{i}\usepackage{cmbright}\Huge\$ . Distribute the subtraction sign to both terms in the subtrahend.

$\displaystyle{9}-{\left(-{2}-{6}{i}\right)}={9}+{2}+{6}{i}\usepackage{cmbright}\Huge\$

Rearrange the terms to put like terms together and then combine like terms.