ANSWER
90 km²
Step-by-step explanation
To find the area of the entire figure we have to find the area of the triangle, the area of the rectangle and then add them.
The top of the figure's length is 18km and the base is 12km long. The base is the length of the rectangle, therefore 18km - 12km = 6km is the height of the triangle. The area of the triangle is:
![A_{\text{triangle}}=(b* h)/(2)=\frac{6\operatorname{km}*6\operatorname{km}}{2}=\frac{36\operatorname{km}^2}{2}=18\operatorname{km}^2]()
The area of the rectangle is:
![A_{\text{rectangle}}=6\operatorname{km}*12\operatorname{km}=72\operatorname{km}^2]()
The area of the entire figure is:
![\begin{gathered} A=A_{\text{triangle}}+A_{\text{rectangle}} \\ A=18\operatorname{km}^2+72^{}\operatorname{km}^2 \\ A=90\operatorname{km}^2 \end{gathered}]()