7 = 2n - 2
n= a number so twice a number is 2n and 7 is 2 less than twice this number.
The acceleration of the bookshelf is equal to 1.30 
<u>Given the following data:</u>
- Mass of bookshelf = 51.5 kilogram
To determine the acceleration of the bookshelf, we would apply Newton's Second Law of Motion:
Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on the object while being inversely proportional to its mass.
Mathematically, Newton's Second Law of Motion is given by this formula;

Substituting the given parameters into the formula, we have;

Acceleration = 1.30 
Read more on net force here: brainly.com/question/1121817
A= 3
b= 4
=3.14(a^2 + ab)
substitute the given a & b values in expression
=3.14((3)^2 + (3*4))
multiply inside parentheses
=3.14(9 + 12)
add inside parentheses
=3.14(21)
multiply
=65.94
ANSWER: 65.94
Hope this helps! :)
C is correct because A is 2.82 and B is 2.8