15 points and a brainliest to the correct ! pls asap
a security alarm requires a four-digit code. the code can use the digits 0–9 and the digits cannot be repeated.

which expression can be used to determine the probability of the alarm code beginning with a number greater than 7?

a) (2p1)(9p3)/10p4

b) (2c1)(9c3)/10c4

c)(10p1)(9p3)/10p4

d)(10c1)(9c3)/10c4

I believe it is LETTER A.
There are 4 spots to be filled and the order matters. When order matters you have to use Permutations (P).
The first spot has a requirement that the number has to be greater than 7. There are only 2 numbers in the set that are greater than 7, 8 & 9.
So for spot 1 you have 2P1.
You have 4 remaining spots to fill and the order still matters so it will be another permutation. Since you cannot use repeats, we only have 9 numbers left to choose from and we are going to fill the 3 slots with these 9 numbers. 9P3
Only choice A has these options

Hello!
volume of sphere =4/3.pi.r^3