8a=4(a-9)
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a = -9

Step-by-step explanation:

8a=4(a-9)

Divide each side by 4

8a/4=4(a-9)/4

2a = a-9

Subtract a from each side

2a-a = a-9-a

a = -9

-9

Step-by-step explanation:

8a = 4(a-9)

Use the distributive property (Multiply 4 times a, and 4 times -9)

8a = 4a - 36

Bring the 4a to the other side

8a - 4a = -36

Add like terms

4a = -36

Divide both sides by 4 to get a by itself

a = -9

there are lots of ways.   pick's theorem tells us if the vertices are lattice points the area a is

a = b/2 + i - 1

where b is the number of boundary lattice points and i is the number of interior lattice points.

in the figure i count b=16, i=50 so

a = 8 + 50 - 1 = 57

let's try the shoelace formula.   the area is half the sum of the cross products of the sides.  

a(-2,6)   -2(2)-6(-5) = 26

b(-5,2)   -5(-3) - 2(-2) = 19

c(-2,-3) -2(-3) - (-3)(4) = 18

d(4,-3)   4(3) - (-3)(5) = 27

e(5,3)   5(3) - 3(1) = 12

f(1,3)     1(6) - 3(-2) = 12

a(-2,6)

each of the cross products is twice the area of the triangle with the associated side and one vertex the origin. so the area of abo=26/2=13.

area = (1/2) (26 + 19 +   18 + 27 + 12 + 12) = 57

that checks!