Function related question with graphs

Question

I will just get straight to the point so I had a test there was question [enter image description here][1]

[1]: https://i.stack.imgur.com/93pAv.jpg can anyone tell why the functions summed up as 1+1+1

Answer 1

You just have to plug in the function values. That is $$ f(f(1)) = f(|2 - |1-3||) = f(0) = |2 - | 0 - 3 | = 1.$$