Answer: 105 grams
Step-by-step equation: they each eat 21 grams a day
The distance between the Earth's surface and the upper edge of the Earth's atmosphere would be Q - V.
The distance from the Sun to the Earth is Q. The distance from the Sun to the upper edge of the atmosphere is V. If you subtract V from Q, the remaining distance is that of the Earth's atmosphere. Q - V = the atmosphere
₇P₅ is a permutation. you can find this setting in the statistics menu of your scientific calculator (i think).
If you don't have a scientific calculator, you can use the following formula:
nPr = 
₇P₅ = 
= 
= 
= 7 * 6 * 5 * 4 * 3
= 2520
Answer: C