physics
posted by mm. .
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

E (per photon) = h c/(wavelength)
I assume you know what h anc d are.
Do the numbers and multipy by a trillion.