The surface area is the area of all the faces of the solid.
So, it is composed by the two triangles (front and rear) and the two lateral rectangles.
The triangles have base 12 and height 8 (both given), so their area is
[tex]A_t=\dfrac{12\cdot 8}{2}=12\cdot 4=48[/tex]
The rectangles have base 14 and height 10 (both given), so their area is
[tex]A_r=14\cdot 10=140[/tex]
Finally, there's a base rectangle with dimensions 14 and 12, which has area
[tex]A_b = 14\cdot 12 = 168[/tex]
The surface area is made of two lateral rectangles, one base rectangle and two triangles, so it is
[tex]S=2A_r+2A_t+A_b=96+280+168=544[/tex]
