Answer:

Step-by-step explanation:

The answer is 509 metres.
The area of the entire sector of DEF = 60 / 360 * PI * radius^2
sector area = 1 / 6 * 3.14159265... * 20^2
sector area =
<span>
<span>
<span>
209.4395102393
</span>
</span>
</span>
segment area = sector area - triangle DEF Area
triangle DEF Area = (1/2) * 20 * sine 60 * 20
triangle DEF Area = (1/2) * 0.86603 * 400
triangle DEF Area = <span><span><span>(1/2) * 346.412
</span>
</span>
</span>
triangle DEF Area =
<span>
<span>
<span>
173.206
</span>
</span>
</span>
segment area = <span>
<span>
209.4395102393
</span>
-173.206
</span>
segment area =
<span>
<span>
<span>
36.2335102393
</span>
</span>
</span>
segment area =
36.23 m
Source:
http://www.1728.org/circsect.htm
In mathematics, 'is' would be the equal sign. And 'of' would be the multiplcation sign. The missing number would be any variable.
56 is 28% of a number would be translated algebraically to:

Solving for x, we get:

Divide 28 on both sides

Multiply 100 on both sides
56 is 28% of 200