Question

Solve each system of equation using substitution

7x + y = 12
Y = 4x - 21

Answer 1

Systems of Equations

We use substitution to solve systems of equations by plugging one equation into the other.

Solving the Question

We're given:

• 
  `7x + y = 12`
• 
  `y = 4x - 21`

y has already been isolated in the second equation. Plug this into the first one:

`7x + (4x - 21) = 12`

Isolate x:

`7x + 4x - 21 = 12\\11x - 21 = 12\\11x= 33\\x=3`

Therefore, x = 3. Plug this into the second equation to solve for y:

`y = 4(3) - 21\\y = 12 - 21\\y = -9`

Therefore, y = -9.

Answer

x = 3

y = -9