We are given the function:

$y = -7x + 5$

To find the output when $x = 15$, substitute $15$ for $x$:

$y = -7(15) + 5$

$y = -105 + 5$

$y = -100$

Final Answer:

$y = -100$

Would you like a step-by-step explanation of how this was solved?

Here are some related questions to practice:

1. Find the output of $y = -7x + 5$ when $x = -3$.
2. Solve for $x$ if $y = 0$ in $y = -7x + 5$.
3. What is the y-intercept of the function $y = -7x + 5$?
4. If $y = -7x + 5$ represents a linear equation, what is its slope?
5. Graph the equation $y = -7x + 5$ and identify its key points.

Tip: The slope of a linear function represents the rate of change of $y$ with respect to $x$.