$\begin {array} {1 1} (a)\;B = 6.6 \: \cos2 \pi \bigg[\large\frac{10^2x}{2.1m} - \large\frac{t \times 10^9 }{11.1s} \bigg]j\: pT & \quad (b)\;B = 6.6 \: \cos2 \pi \bigg[\large\frac{x}{3.33m} - \large\frac{t \times 10^{10} }{1.11s} \bigg]j\: pT \\ (c)\;B = 2.2 \: \cos2 \pi \bigg[\large\frac{x}{1.65m} - \large\frac{t \times 10^9 }{1.11s} \bigg]j\: pT & \quad (d)\;B = 3.3 \: \cos2 \pi \bigg[\large\frac{x}{3.3m} - \large\frac{t \times 10^9 }{2.22s} \bigg]j\: pT \end {array}$