${{t}_{1}}=0\,\Rightarrow \,{{\Phi }_{1}}=0$ ${{t}_{2}}=2s\,\Rightarrow \,{{\Phi }_{2}}=0/2\times {{2}^{2}}+0/3\times 2=0/8+0/6=0/4Wb$ $\left| \overline{\varepsilon } \right|=\left| -N\frac{\Delta \Phi }{\Delta t} \right|\Rightarrow \left| R\overline{I} \right|=\left| -N\frac{\Delta \Phi }{\Delta t} \right|\Rightarrow R\times 1/4=20\times \frac{1/4-0}{2-0}\Rightarrow R=10\Omega $