\(\textbf{41 a)}\)
\begin{aligned}3 \mathrm{km / h} &=\frac{3000 \mathrm{\,m} / \mathrm{min}}{60} . \\&=50 \mathrm{\,m} / \mathrm{min}\\\text { In } 10 \text { minutes }&\text{walk is } 50 \times 10=500 \mathrm{\,m}\\&\therefore 5 \mathrm{\,cm}=500 \mathrm{m\,}\\&1 \mathrm{\,cm}=100\mathrm{\,m}\\\end{aligned}
\(\textbf{41 b)}\)
\begin{aligned}\text { Scale: } 1 \mathrm{\,cm}&=100 \mathrm{\,m} \\\text { Area }&=\frac{400}{2}(100+300) \\&=80000 \mathrm{\,m}^{2} \\20 \mathrm{\,mm}&=0.02 \mathrm{\,m} \\\therefore \text { Volume } &=80000 \times 0.02 \\&=1600 \mathrm{\,m}^{3}\end{aligned}
