Answer :
Explanation :

9 P in SS  is a short form for 9 Planets i  Solar System.   There are many more of this kind. Some of them are:   1. 7 C in a R        -    7 Colours in a Rainbow 2.  90 D in a R A   -    90 Degrees in a Right Angle 3.  52 W in a Y     -    52 Weeks in a Year 4.  5 C in an OF 5.  12 S of the Z