Answer
$n(P\cup N')=90$
This value represents the number of pharmaceutical stocks or not unchanged (i.e. changed) stocks, or both.
Work Step by Step
$n(S)=100,~~n(P)=50,~~N(n)=40$
$n(N')=n(S)-n(N)=100-40=60$
$n(P\cap N')=n(P \cap V)+n(P \cap D)=10+10=20$
$n(P\cup N')=n(P)+n(N')-n(P\cap N')=50+60-20=90$
This value represents the number of pharmaceutical stocks or not unchanged (i.e. changed) stocks, or both.