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
1.8 x 10^9 = 1,800,000,000
8.7 x 10^7 = 87,000,000
1.8 x 10^9 > 8.7 x 10^7
Five hundred seventy thousand and twenty