Frequency Spectrum Analysis
The magnitude is given by $ {\left| X \left( f \right) \right|} $ hence it is 6.
Assuming all data is given in the graph, the function isn't complex it is only negative -> Phase is -180 degrees.
You should use its symmetry. Without over thinking it, It could be generated by a window on the center convolved with 2 deltas (Shifted) -> Sinc in time multiplied by 2 exponentials.