First you want to divide the triangle into 7 equal triangles.
Since the height of each of these 7 triangles divides each of them in half we get 14 trangles with height of 27 and base of 13 (this is because the original side is divided into two halves: 26/2=13.)
To find the area of one of the triangles we will use the formula:
where b is the base and h is the height.
Plugging in the values that we have into the formula, we get
which gives us 175.5
Since there are 14 of these triangles in total, we must multiply this number by 14 so we get
which ends up with our answer: 2457mm
Choice C is your answer.