GSM networks use microwaves of 20 cm in wavelength.

The energy carried by one trillion (1012) photons of this wavelength is closest to ...

a. 10^-16 Joules
b. 10^-15 Joules
c. 10^-14 Joules
d. 10^-13 Joules
e. 10^-12 Joules

find the energy in one photon using plancks constant, speed of light and wavelength.

multiply by a trillion