20% because:
rate of Increase = ( final - initial ) / initial * 100
rate of increase = ( 12 - 10 ) / 10 * 100
rate of Increase = 2 / 10 * 100
rate of Increase = 20
To calculate the area of the black material on the flag, we need the shape and the dimensions of the black material itself.
<em>Since the question is incomplete, as the dimension of the flag and the dimension of the black material are not given, I will provide a general explanation</em>
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Assume the shape of the black material is a rectangle.
The area will be calculated as:

Take for instance;

The area is:


Assume the shape of the black material is a square.
The area will be calculated as:

Take for instance;

The area is:


Assume the shape of the black material is a triangle
The area will be calculated as:

Take for instance;

The area is:


So, in general.
You need to first get the shape of the black segment on the flag, then calculate the area using the appropriate formula.
Related link:
brainly.com/question/24251781
Answer:
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Step-by-step explanation:
the area of a triangle is
baseline × height / 2
we have here 2 triangles : the larger, outer shaded one, and the smaller, inner white one.
to get the area of the shaded part, we need to calculate the area of the large triangle and subtract the area of the smaller triangle.
large area :
12 × 15 / 2 = 6 × 15 = 90 ft²
small area :
8 × 10 / 2 = 4 × 10 = 40 ft²
the shaded area is
90 - 40 = 50 ft²