Hello!
We have the following data:
f (radiation frequency) = [tex] 3.0*10^{19}\:Hz [/tex]
v (speed of light) = [tex] 3.0*10^8\:m/s [/tex]
λ (wavelength) = ? (in m)
Let's find the wavelength, let's see:
[tex] f = \dfrac{v}{\lambda} [/tex]
[tex] 3.0*10^{19} = \dfrac{3.0*10^8}{\lambda} [/tex]
[tex] \lambda = \dfrac{3.0*10^8}{3.0*10^{19}} [/tex]
[tex] \boxed{\boxed{\lambda = 1*10^{-11}\:m}}\Longleftarrow(wavelenght)\end{array}}\qquad\checkmark [/tex]
I Hope this helps, greetings ... DexteR! =)