The perimeter of the triangular end is 12 m, so the total rectangular area is
.. (12 m)*(8 m) = 96 m^2
There are two triangles with base 3 m and height 4 m, so their total area is
.. (3 m)*(4 m) = 12 m^2
The surface area of the figure is the sum of these
.. 96 m^2 +12 m^2 = 108 m^2