Question

-4x+6y=-18 and y=-2x+21

Answer 1

x=9, y=3

Explanation:

For this problem, you can sub the second equation for y in the first one.

This gives -4x+6(-2x+21)=-18, which can be expanded to -4x-12x+126=-18.

From there, you can collect like terms to get -16x+126=-18.

Subtracting 126 from both sides gives -16x=-144.

You want to isolate x by dividing both sides by -16, giving x=9.

You can sub 9 for x in either equation to work out y (I'm using the second one, as it is easier).

This gives y=-2×9+21, which can be solved to y=-18+21, or y=3.

**This question involves solving linear equations, which you may wish to revise. I'm always happy to help!

Answer 2

(9, 3)

General Formulas and Concepts:

Pre-Algebra

Order of Operations: BPEMDAS

1. Brackets
2. Parenthesis
3. Exponents
4. Multiplication
5. Division
6. Addition
7. Subtraction

• Left to Right

Distributive Property

Equality Properties

• Multiplication Property of Equality
• Division Property of Equality
• Addition Property of Equality
• Subtraction Property of Equality

Algebra I

• Coordinates (x, y)
• Solving systems of equations using substitution/elimination

Explanation:

Step 1: Define Systems

-4x + 6y = -18

y = -2x + 21

Step 2: Solve for x

Substitution

1. Substitute in y [1st Equation]: -4x + 6(-2x + 21) = -18
2. [Distributive Property] Distribute 6: -4x - 12x + 126 = -18
3. [Subtraction] Combine like terms: -16x + 126 = -18
4. [Subtraction Property of Equality] Subtract 126 on both sides: -16x = -144
5. [Division Property of Equality] Divide -16 on both sides: x = 9

Step 3: Solve for y

1. Substitute in x [2nd Equation]: y = -2(9) + 21
2. Multiply: y = -18 + 21
3. Add: y = 3