In this problem I see two big triangles so there total height is 11.9 and there base is 16.8 and we can plugh that in the formula for the area of a triangle but we need to divide the height by two....
11.9/2 = 5.95
So 12∗5.95∗16.8=49.98
(Note) I with that answer I completed the necessary division... already so 49.98 * 2 = 99.96ft2