Solve, using the substitution method.
y – 3x = 7
21 + 9x = 3y

a. there is no solution.

b. there are an infinite number of solutions.

c. the solution is (1, 10)

d. the solution is (28, 0)

The answer is B

let me show my answer

-3x+y=7;9x+21=3y

Solve -3x+y=7 for y

Add 3x to  both sides

-3x+y+3x=7+3x

y=3x+7

Substitute 3x+7 for y in 9x+21 =3y

9x+21=3y

9x+21=3(3x+7)

Simplify both sides of the equation

9x+21=9x+21

Add -9x to both sides

9x+21+-9x=9x+21+-9x

21=21

Add -21 to both sides

21+-21=21+-21

0=0

Answer : B , Infinitely many solutions

I hope that's help !

Have a great day !

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