Looking at the figure, we can see that the lateral rectangles have a missing value (the horizontal length), but these were previously together with the sides of the triangle, so the lengths are 7 cm.
Now, we have two identical triangles and one big rectangle in the middle with dimensions 17cm×26 cm. The area of the triangles are:
[tex]A_{\text{triangle}}=\frac{12\cdot3.6}{2}=21.6\operatorname{cm}^2[/tex]
And for the rectangle:
[tex]A_{\text{rectangle}}=17\cdot26=442\operatorname{cm}^2[/tex]
The total area is:
[tex]\begin{gathered} A_{\text{Total}}=A_{\text{rectangle}}+2A_{\text{triangle}}=442+2\cdot21.6 \\ \therefore A_{Total}=485.2\operatorname{cm}^2 \end{gathered}[/tex]
