Consider the circle with center X, as shown in the figure.
Draw the diameter of the circle which is parallel to cherd AB, as shown in the figure.
Since the diameter and AB are parallel, then the line segment XC which bisects AB at C, will be perpendicular to AB.
SO triangle XCB is a right triangle. Thus the length of CX, by the Pythagorean theorem is

units.
Answer: 8 units
Where is the list of triangle parts? I can help you if I see it
You need to make the right side = 0
To do this you subtract 10 from both sides of the equation:-
x^2 + 6x + 9 - 10 = 10 - 10
x^2 + 6x - 1 = 0
The width is the rectangle is w. Since the length is 25 feet larger than the width, it will be w+25
Perimeter for rectangle formula:2(L+W)
2(w+25+w)= 4w+50