Based on the provided multiple regression results, the coefficient of $X_4$ is $-9.976$, with a p-value of $0.024$, indicating statistical significance (since $p < 0.05$). When $X_4 = 1$, its effect on the dependent variable is to decrease it by $9.976$ units because the coefficient is negative. Therefore, the correct answer is:

The dependent variable will decrease by 9.976 units.

Would you like a detailed breakdown or have additional questions?

Here are some follow-up questions for further exploration:

1. What does the statistical significance of $X_4$ imply about its role in the model?
2. How does the standard error influence the interpretation of $X_4$'s coefficient?
3. What would the interpretation be if $X_4$ had a p-value greater than 0.05?
4. How do the effects of the other variables ($X_1, X_2, X_3$) compare to $X_4$?
5. What steps should be taken to evaluate the overall fit of this regression model?

Tip: Always check the p-value to determine the statistical significance of a coefficient before interpreting its effect.