E = h c / ʎ
where,
h is the Planck’s constant = 6.626 x 10⁻³⁴ m² kg / s
c is the speed of light = 3 x 10₈ m/s
ʎ is the wavelength of light = 150 nm = 150 x 10⁻⁹ m
Now pot the values in equation;
E = (6.626 x10⁻³⁴ m² kg / s) x (3 x 10⁸ m/s) / (150 x 10⁻⁹ m)
E = 1.325 x 10⁻¹⁸ J
Now by using the following equation we can calculate the frequency;
E = hf
f = E/h
f = 1.325 x 10⁻¹⁸ / 6.626 x 10⁻³⁴
f = 1.9997 x 10¹⁵ Hz
