Answer:138
Step-by-step explanation:
1 joule = 6,242e+18ev
20 joule = 20 joule *6,242e+18 ev/joule =1,248e+20 ev
1,248e+20 ev / (10 ev / photon) =1,248e+19 photons.
7 divided by 2 is 3.5 therefore the answer is:3.5
The answer is 20. I hope this helps.