Answer
$9.4\times 10^{14}s^{-1}$ to $1.1 \times 10^{15}s^{-1}$
Work Step by Step
We us the formula
$f =\frac{c}{λ},$
where $c$ is the speed of light and $\lambda$ is the wavelength ($280-320$ nm for UV B light).
$f_1=\frac{3\times 10^8}{280\times 10^{-9}}\approx 1.1\times 10^{15}s^{-1}$
$f_2=\frac{3\times 10^8}{320\times 10^{-9}}\approx 9.4\times 10^{14}s^{-1}$
The frequency range of light that octyl methoxycinnamate and oxybenzone compounds (common in sunscreen) absorb is from $9.4\times 10^{14}s^{-1}$ to $1.1 \times 10^{15}s^{-1}$.
