Point a is the center of this circle.

the ratio of the lengths of (ef/bc) and (ad/ih) is 2: 1.

Given is a circle A with points B, C, D, E, F, and I on its circumference.

A line joining any two points on circumference of any circle is called a chord of the circle. Here BC, EF, and HI are chords of the circle.

A line joining center A and any point on circumference of the circle is called radius of the circle. Here AD is the radius of the circle.

Any chord that is passing through the center of the circle is called the diameter of the circle. Here EF and HI are diameters of the circle.

A diameter is always twice the length of radius. So ratio of diameter to radius will be 2:1.

Hence, ratio of the lengths EF and AD will be 2:1

Line segment FE and HI are the diameters of the circle and are equal. Line segment AD, EA, AH and AI are the radius and are equal. Always remember that halved the diameter is the radius or twice the radius is the diameter.

$8

Step-by-step explanation:

You divide 7 by 7 and 56 by 7, 56 divided by 7 is 8, therefore the unit rate is $8 per book.