First we find the measurement of dark dot .
ANd for that we have to use the formula of the angle formed by the intersection of chord .
Let the dark dot be t.
So we have

t and z are linear pair and sum of angles of linear pair =180 degree.
So we get

When I put it in my calculator I got d=5
Answer:
864 ft^2.
Step-by-step explanation:
Area of the base = 16^2 = 256.
Area of the triangular sides = 4 * 1/2 * 16 * 19
Total area = 256 + 608
= 864 ft^2.