Answer: Option C
Explanation:
Clearly, the child moves from A to B 90 metres eastwards upto B, then turns right and moves 20 metre upto C, then turns right and moves upto 30 metre upto D. Finally he turns right and moves upto 100 metre upto E.
So AB = 90 metre, BF = CD = 30 metre,
So, AF = AB - BF = 60 metre
Also DE = 100 metre, DF = BC = 20 metre
So, EF = DE - DF = 80 metre
as we can see in image that triangle AFE is a right angled triangle and we are having two sides, need to calculate third one, so we can apply Pythagoras theorem here
\begin{aligned}
A = AE = \sqrt{AF^2 + EF^2} \\
= \sqrt{(60)^2+(80)^2} \\
= \sqrt{3600+6400} \\
= \sqrt{10000} = 100
\end{aligned}
So from starting point his father was 100 metre away.