No it’s not because (6,2) would be a no solution so no
10-4=6
3*2k= 6k
6k=6
K=1 is the answer
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
The degree of vertex b is b