Arrow Area

Since it is an arrow, we can assume that lengths of the slanted line segments are equal.

Now, sum of length of non-slanted line segments is $10$ , so remaining should be $20-10$ = $10$ , hence slanted line segments are both length of $5$ .

Now we can split this arrow into composite of triangle and rectangle. The area of rectangle is $3\times2 = 6$

For area of triangle, we can use Heron's Formula . Result should be approximately $9.165$

So the sum of these areas is $\boxed{15.165}$

Length of slanted line segments = 5

Drop a perpendicular from the tip of the arrow to the base of the triangle. One side is 2, the hypotenuse is 5, so the height = 4.5825 and the triangle area is 9.165. Rectangle area = 6, so total area = 15.165