Answer :
[tex]\begin{gathered} p\text{ = 344m} \\ L\text{ = 98m} \\ B=\text{?} \\ P\text{ = 2(L+B)} \\ 344\text{ = 2(98 + B)} \\ 344\text{ = 196 + 2B} \\ 344-196\text{ = 2B} \\ 148\text{ = 2B} \\ B\text{ =}\frac{148}{2}\text{ = 74}m \\ \end{gathered}[/tex]