Yes, your friend is correct in using the Multiplication Property of Equality to solve the equation $3x = 15$.

Justification:

The Multiplication Property of Equality states that if you multiply or divide both sides of an equation by the same non-zero number, the equality is preserved.

To solve $3x = 15$, the goal is to isolate $x$. You can do this by dividing both sides of the equation by 3 (the coefficient of $x$):

$\frac{3x}{3} = \frac{15}{3}$

This simplifies to:

$x = 5$

Therefore, your friend is correct because they are applying the Multiplication Property of Equality to isolate $x$.

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Would you like to go over any of these details? Here are some related questions to explore further:

1. What is the Multiplication Property of Equality?
2. How do you handle equations where the variable has a coefficient of zero?
3. Can you apply this property to equations involving fractions?
4. What if the equation was $3x = -15$? How would that affect the solution?
5. How does this property differ from the Addition Property of Equality?

Tip: When solving linear equations, always check your solution by substituting it back into the original equation.