IMO C:

Please confirm ,i will give explanation after confirmation

(p-n)(p+n) is divisible by 15 ( 3 and 5 )or not..

A: it says remainder p+n is divided by 5 is 1.

7 + 4 =11 /5 ->reminder = 1 p-n= 3

8+4 = 11 /5-> reminder =1 p-n = 5

So A is not suff.

B:

remainder p-n is divided by 3 is 1

5 -4 = 1/3->reminder = 1 p+n = 9 divisible by 3

8-4 =1/3->reminder = 1 p+n=12 divisible by 3.

12-2=10/3->reminder=1 p+n= 14 not divisible by 3 or 5 but p-n is divisible by 5

So B is not suff.

A+ B

yes its suff. check it

Thanks