The use of high-speed of circuit-breakers

Reactance relay is normally preferred for protection against

A first order system is initially at rest and excited by a step input at time $$t=0.$$ Its output becomes $$1.1$$ $$V$$ is in $$4$$ seconds and eventually reaches a steady state value of $$2V$$. Determine its time

Compute the amplitude of the fundamental component of the waveform given in figure.