The circuit loop in Figure 6 is situated in a magnetic field of magnetic flux density \boldsymbol{B}=\hat{z} 3 \cos \left(5 \pi x 10^{7} t-\frac{2}{3} \pi x\right) Assume R = 15ohms, find the current i. \text { Hint: Must integrate } \mathrm{d} \Phi=\mathbf{d B} \cdot d \mathbf{A} \text { over the surface before finding } \mathrm{d} \Phi / \mathrm{dt} \text {. }