Answer
$\varepsilon=0.0V$
Work Step by Step
Remember that the induced emf is equal to $$\varepsilon=\frac{d \phi}{dt}=\frac{d}{dt} \int \vec{B} d\vec{A}$$ There is no change in area or magnetic field between $t=2.0s$ and $t=4.0s$, therefore, the change in flux is 0 and the induced emf is zero.
