The vertical intercept (also known as the y-intercept) is where the line crosses the y-axis. At this point, $x = 0$.

The equation of the graph is:

$y = 18 - 3x$

To find the vertical intercept, substitute $x = 0$ into the equation:

$y = 18 - 3(0)$ $y = 18$

Thus, the vertical intercept is $18$. This means that at week 0, Juliana owed her brother $18.

Would you like further clarification or a detailed explanation on how intercepts work? Let me know! Here are some follow-up questions to expand on this concept:

1. What does the slope of the line represent in this situation?
2. How many weeks will it take Juliana to repay the full amount?
3. If the repayment rate doubled, what would the new equation be?
4. What happens to the graph if Juliana borrowed $30 instead?
5. How do you find the horizontal intercept from this equation?

Tip: The vertical intercept always represents the initial value in a real-world context like this one.