Faraday’s law

A rectangular coil with 80 turns and area $2.5\times10^{-3}\,\text{m}^2$ is placed in a uniform magnetic field. The magnetic flux density through the coil decreases uniformly from 0.40 T to 0.10 T in 0.020 s. What is the magnitude of the average induced e.m.f. in the coil?

Use $\varepsilon = N\,\Delta(BA)/\Delta t$.