Correct.

$\displaystyle{40}{{c}}^{{6}}={2}\cdot{2}\cdot{2}\cdot{5}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\usepackage{cmbright}\Huge\$

$\displaystyle{48}{{c}}^{{7}}={2}\cdot{2}\cdot{2}\cdot{2}\cdot{3}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\usepackage{cmbright}\Huge\$

GCF $\displaystyle={2}\cdot{2}\cdot{2}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}\cdot{c}={8}{{c}}^{{6}}\usepackage{cmbright}\Huge\$

The missing exponent is 6.