Solve by the method of your choice (addition or substitution)

Question

7x-4y=9

2x+y=9

Answer 1

7x -4y = 9

2x +y = 9

multiply the bottom equation by 4

7x -4y = 9

8x +4y = 36

add the equations

7x -4y = 9

8x +4y = 36

15x +0y = 45

simplify and solve for x

15x = 45

x = 3

pick one of the equations

2x +y = 9

enter the value for x

2(3) +y = 9

solve for y

6 +y = 9

y = 3

Answer:  x = 3, y = 3

check:

7x -4y = 9

7(3) -4(3) = 9

21 -12 = 9  True

check

2x +y = 9

2(3) +3 = 9

6 + 3 = 9 True

Answer 2

Given equations are 7x - 4y = 9 ---> (1)

2x + y = 9

Substract 2x  from each side.

y  = -2x + 9 ---> (2)

From (2) substitute the y  value in (1).

7x - 4(-2x + 9) = 9

7x + 8x - 36 = 9

15x  = 45

Divide each side by 15.

x = 3.

Subsstitute x  value in (2).

y  = -6+9

y  = 3

Solution x  = 3, y  = 3.