Answer:
37.68
Step-by-step explanation:
c = 2 x 3.14 x 6
4x - 24 = -2x + 30
4x + 2x = 30 + 24
6x = 54
x = 9
answer: the number is 9
The relationship between the cost of books and pens is an illustration of linear equation.
The linear equation is (a) 
From the question, we have:
x exceeds 2 times y by 10
Rewrite as:
x exceeds 2y by 10
Exceed means plus (+)
So, we have:

Equate the above equation to 0

Hence, the required equation is (a) 
Read more about linear equation at:
brainly.com/question/11897796
Upper + Lower surface area= 2(12*12-36)=216cm^2
Side surface area=6*4*4=96+12*4*2=192
Total surface area= 216+192=408cm^2