It appears that you used the Pythagorean Theorem with 1 and 9 as the legs. However, the ramp is the hypotenuse of the right triangle. The correct equation to use is: $\displaystyle{{1}}^{{2}}+{{d}}^{{2}}={{9}}^{{2}}\usepackage{cmbright}\Huge\$ . The correct answer is $\displaystyle\sqrt{{80}}\usepackage{cmbright}\Huge\$ .