#### Answer

$3.84*10^{14}s^{-1}$

#### Work Step by Step

Plugging in the value of $7.80*10^-7m$ as the wavelength into the equation $f=\frac{c}{\lambda}$ where $f$ is frequency in $s^{-1}$, $c$ is the speed of light ($2.998*10^8 m/s$), and $\lambda$ is the wavelength in $m$ gives a value of $3.84*10^{14}s^{-1}$ for the frequency.