Answer: S=25
Explanation:
Given: Total creepy-crawly creatures in a room=20
Also, there are 20 % are spiders.
Since 20%=0.2
The number of spiders=

Then number of flies= 20-4=16
Since flies has 6 legs, then the number of legs in all flies=

Also, spider has 8 legs, then the number of all legs in spiders=

Total legs of all creepy crawls= 96+32=128
The percent of spider legs=

hence, if S% of the total legs belong to spiders, then S=25