Triangles have 3 vertices. The total is 21 vertices. 21 / 3 = 7. He drew 7 triangles.
The equation (1) is divided by 2 to create new equivalent system of equations.
Step-by-step explanation:
The given systems of equations are:

Considering 8y instead of 8 in eq(1)
We need to identify what action was completed to create this new equivalent system of equations? 
Comparing given equations we came to know that equation(1) is divided by 2 to get the new equation i.e

While second equation is same as given.
So, The equation (1) is divided by 2 to create new equivalent system of equations.
Keywords:System of Equation
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Answer:
D
Step-by-step explanation:
Its D because A is all 90 degrees
Not C because all 90
The correct answer is B because after you simplifiy the expression, you would get that answer:
7x + 3y - 2 + 6x + 1 + y^2
combine all the like terms to one side first
7x + 6x - 2 + 1 + y^2
then simplify
13x - 1 + y^2 or y^2 + 3y + 13x - 1