After substituting for $y$ in $4x + y = 29$, simplify. What kind of equation in $x$ do you get?

Once you have the quadratic in standard form, factor it (if possible) or use another method to solve. You will get two $x$-values—check which one appears in the answer choices.

In Desmos, type the two equations as

• y = 29 - 4x (this is the same as $4x + y = 29$)
• y = 50 - x^2

Look at where the line and the parabola cross. Click on each intersection point; Desmos will show the coordinates $(x, y)$.

Note the $x$-coordinates of the intersection points. Compare those $x$-values to the answer choices and select the one that appears.

You are told that $y = 50 - x^2$.

From the first equation, $4x + y = 29$. Substitute $50 - x^2$ for $y$:

Now you have an equation with only $x$.

Simplify the equation:

Subtract $29$ from both sides:

Reorder the terms to get standard quadratic form $ax^2 + bx + c = 0$:

Multiply both sides by $-1$ to make the $x^2$ term positive:

Factor $x^2 - 4x - 21$.

You need two numbers that multiply to $-21$ and add to $-4$. Those numbers are $-7$ and $3$.

So the factorization is:

Set each factor equal to zero:

So the possible $x$-values are:

The two intersection $x$-values are $7$ and $-3$.

Look at the answer choices: $7$ is not listed, but $-3$ is.

Therefore, a possible value of $x$ is $-3$.