This problem can be answered using the equation below:
c = frequency x wavelength
where: c is the speed of light, which is equal to 3.00 x 10^8 m / s
frequency = c / wavelength
= (3.00 x 10^8m /s) / (2.40 x 10^-5 cm x 1 m /100cm)
= (3.00 x 10^8 m/s) / 2.40 x 10^-7m
= 1.25 x 10^15/s 1 / s = 1Hz
Frequency = 1.25 x 10^15Hz