Exercise:
Two circular figures $R_1$ and $R_2$ are represented in the image, respectively with radius $r_1 = 21,2cm$ and $r_2 = 32,2cm$. In $R_1$ there is a uniform magnetic field $B_1 = 48mT$ in the perpendicular direction coming in the sheet, and a uniform magnetic field $B_2 = 77.2mT$ in perpendicular direction leaving the sheet (all effects on the edge are neglected). Both fields decrease by $8.5mT / s$. Calculate $\int \vec{E}\cdot d\vec{s}$ for each of the three paths shown in the figure.
How can i approach this problem? I don't understand what kind of reasoning i have to do about the decreasing of the magnetic field. Thanks