A child went 90 feet in the west to look for his father, then he turned right and went 20 feet. After this, he turned right and walked 30 feet to reach his uncle's house. His father was NOT there. From there he went 100 feet to his south and met his father. How far did he meet his father from the starting point?

The logic followed here is:-

1) A child went 90 feet in the west.

2) He turned right and went 20 feet.

3) Then again turned right and walked 30 feet.

4) Finally he turned south and went 100 feet.

Drawing the diagram according to the given information:

So, the total least between the starting point and endpoint is: 

\({ \ \sqrt{80^2 +60^2} }\)  = \({ \sqrt{6400 + 3600} }\) =\({ \sqrt{10000} }\) = 100

Hence, '100 feet' is the correct answer.