Solve using substitution. $$ \begin{array}{l}-3 x-3 y=12 \ y=-7\end{array} $$

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Solve the system of equations by following steps:
- step0: Solve using the substitution method:
  $$\left\{ \begin{array}{l}-3x-3y=12\y=-7\end{array}\right.$$
- step1: Substitute the value of $$y:$$
  $$-3x-3\left(-7\right)=12$$
- step2: Multiply the numbers:
  $$-3x+21=12$$
- step3: Move the constant to the right side:
  $$-3x=12-21$$
- step4: Subtract the numbers:
  $$-3x=-9$$
- step5: Change the signs:
  $$3x=9$$
- step6: Divide both sides:
  $$\frac{3x}{3}=\frac{9}{3}$$
- step7: Divide the numbers:
  $$x=3$$
- step8: Calculate:
  $$\left\{ \begin{array}{l}x=3\y=-7\end{array}\right.$$
- step9: Check the solution:
  $$\left\{ \begin{array}{l}x=3\y=-7\end{array}\right.$$
- step10: Rewrite:
  $$\left(x,y\right) = \left(3,-7\right)$$
To solve the system of equations using substitution, we have the following equations:

1. $$ -3x - 3y = 12 $$
2. $$ y = -7 $$

### Step 1: Substitute the value of $$ y $$

From the second equation, we know that $$ y = -7 $$. We can substitute this value into the first equation.

### Step 2: Substitute into the first equation

Substituting $$ y = -7 $$ into the first equation:

$$
-3x - 3(-7) = 12
$$

### Step 3: Simplify the equation

Now, simplify the equation:

$$
-3x + 21 = 12
$$

### Step 4: Isolate $$ x $$

Next, isolate $$ x $$:

$$
-3x = 12 - 21
$$
$$
-3x = -9
$$

### Step 5: Solve for $$ x $$

Now, divide both sides by -3:

$$
x = 3
$$

### Final Solution

Thus, the solution to the system of equations is:

$$
(x, y) = (3, -7)
$$
$$ x = 3 $$ and $$ y = -7 $$.

Solve using substitution. \( \begin{array}{l}-3 x-3 y=12 \\ y=-7\end{array} \)

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