-8a-3b+6b-5a+9b= -13a-18b
-8a-5a=-13a
3b+6b+9b=18b
Hopes that helps
From what I can pick up from your problem statement, you want to know "<span>a similar charm has a diameter of 4 cm what is the circumference." Please, would you use proper punctuation in your writing, for greater clarity:
"A</span><span> similar charm has a diameter of 4 cm. What is the circumference?"
The formula for the circumference of a circle, when the diameter is known, is
C=</span>

d or C=pi*d
In this case, with diamter 4 cm, the circumference, C, is 4pi cm.
The answer should be 390=60s, assuming s is the number of shelves he would need.
By the way, if you want the answer using this formula:
390=60s
390/60=s
6.5=s
s=6.5
Step-by-step explanation:
slope = (y2-y1) / (x2-x1)
equation of the line y2 - y1 = m(x2-x1),
y2 = m(x2-x1) +y1
y2-y1 = -2(x2- (-3))
y2-y1 = -2x -6
y2 - 1 = -2x -6
y2 = -2x -5
Remember:
a) (x,y) => (x, -y) is a reflection across X axis
b) (x,y) => (-x,y) is a reflection across Y axis
Here △RST is mapped to △R′S′T′ using the rule (x,y)→(x,−y)
Hence it is a reflection across X axis.
The size of the triangle does not alter.
But when this is followed by (x,y)→(3x,3y), the lengths increase by a factor 3.
Hence the triangles do not remain congruent.
△RST is not congruent to △R′S′T′ because the rules do not represent a sequence of rigid motions.
Option A) is the right answer