Can you add the picture to the question?
Answer: 21.44 cm
Step-by-step explanation:
Given
Radius r=15 cm
distance of chord from the center is 10 cm
From the figure, the length of the chord is AC
Applying Pythagoras

The length of the chord is 
8 × 5 = 40
So the border has to be 40 feet.
Hope this helps!
Work:
length × width = answer
length = 8
width = 5
answer = 40
Solve the equation for y
x-3y= -18
-3y = -18-x
now, divide both sides with -3
y = (-18-x)/-3
y = 6 +x/3
your slope is 1/3
and y-intercept is 6
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