88 is between the perfect squares 81 and 100. So $\displaystyle\sqrt{{{88}}}\usepackage{cmbright}\Huge\$ is between $\displaystyle\sqrt{{{81}}}\usepackage{cmbright}\Huge\$ and $\displaystyle\sqrt{{{100}}}\usepackage{cmbright}\Huge\$ .

$\displaystyle\sqrt{{{81}}}={9}\usepackage{cmbright}\Huge\$ and $\displaystyle\sqrt{{{100}}}={10}\usepackage{cmbright}\Huge\$

Because 88 is closer to 81 than it is to 100, $\displaystyle\sqrt{{{88}}}\usepackage{cmbright}\Huge\$ is probably about 9.3 or 9.4.

$\displaystyle{9.3}\cdot{9.3}={86.49}\usepackage{cmbright}\Huge\$ and $\displaystyle{9.4}\cdot{9.4}={88.36}\usepackage{cmbright}\Huge\$

88 is closer to 88.36 than 86.49, so the answer is 9.4.