You may have subtracted 45 from 420 instead of subtracting $\displaystyle{45}-{\left(-{420}\right)}\usepackage{cmbright}\Huge\$ . If a place is 420 meters below sea level, the elevation is $\displaystyle-{420}\usepackage{cmbright}\Huge\$ meters. The correct answer is that Athens is 465 meters higher than the Dead Sea.