48 is between the perfect squares 36 and 49. So $\displaystyle\sqrt{{{48}}}\usepackage{cmbright}\Huge\$ is between $\displaystyle\sqrt{{{36}}}\usepackage{cmbright}\Huge\$ and $\displaystyle\sqrt{{{49}}}\usepackage{cmbright}\Huge\$ .

$\displaystyle\sqrt{{36}}={6}\usepackage{cmbright}\Huge\$ and $\displaystyle\sqrt{{{49}}}={7}\usepackage{cmbright}\Huge\$

Because 48 is very close to 49, $\displaystyle\sqrt{{{48}}}\usepackage{cmbright}\Huge\$ is probably about 6.9 or 7.0.

$\displaystyle{6.9}\cdot{6.9}={47.61}\usepackage{cmbright}\Huge\$ and $\displaystyle{7.0}\cdot{7.0}={49.00}\usepackage{cmbright}\Huge\$

48 is closer to 47.61 than 49.00, so the answer is 6.9.