Step-by-step explanation:
in that case we can imagine a diagonal line DB that splits the quadrilateral into 2 right-angled triangles: ADB and CDB.
the area of the quadrilateral is then the sum of the areas of the 2 triangles.
the area of a right-angled triangle is
leg1 × leg2 / 2
with the legs being the sides that enclose the 90 degree angle.
so, for ADB we get
AD × AB / 2 = 3 × 11 / 2 = 33/2 = 16.5
for CDB we get
BC × CD / 2 = 7 × 9 / 2 = 63/2 = 31.5
so, in total for the area of the quadrilateral we get
16.5 + 31.5 = 48
