Respuesta :
The cross section of the canal will form a trapezoid. First, find the area of the cross section. The area of a trapezoid is defined as
[tex]\begin{gathered} A_{\text{trapezoid}}=\frac{a+b}{2}h \\ \\ \text{Given} \\ h=2\text{ meters (2 meters deep)} \\ a=4\text{ meters (4 meters wide)} \\ b=2\text{ meters (2 meters wide at the bottom)} \end{gathered}[/tex]Substitute the following values and we get the area
[tex]\begin{gathered} A=\frac{a+b}{2}h \\ A=\frac{4+2}{2}(2) \\ A=\frac{6}{2}(2) \\ A=6\text{ m}^2 \end{gathered}[/tex]Now that we have the area of the cross section, multiply it to the length of the irrigation canal.
[tex]\begin{gathered} \text{Before multiplying, all units must be the same, convert km to meters} \\ 10\operatorname{km}\rightarrow10,000\text{ meters} \\ 6\text{ m}^2\times10000\text{ meters} \\ \Longrightarrow60000\text{ m}^3 \end{gathered}[/tex]Therefore, they have to excavate 60,000 cubic meters of earth to make the canal.
