Let's analyze the given situations and match them to their respective equations.

Situations and Equations:

1. Leilah has not yet studied 600 of her 2400 flashcards. She studies 40 new cards each day.
   Equation: $(600 + 40)x = 2400$
   Explanation: The 600 cards represent the ones she has left to study, and she studies 40 cards per day. Thus, $600 + 40x = 2400$, where $x$ is the number of days.

2. Stetson rents studio space for $600 a month for music lessons. He charges his students $40 per hour and earned a profit of $2400 this month.
   Equation: $2400 - 40x = 600$
   Explanation: The profit Stetson makes after charging $40 per hour is $2400, and he needs to account for the $600 rent. Thus, $2400 - 40x = 600$, where $x$ is the number of hours he worked.

3. A kit contains 600 letter tiles and 40 number tiles. Each tile has the same mass, and the kit has a total mass of 2400 g.
   Equation: $40x - 600 = 2400$
   Explanation: The 600 letter tiles and 40 number tiles contribute to the total weight of 2400 grams, where $x$ represents the mass per tile.

Final Matching:

1. Leilah's situation: $(600 + 40)x = 2400$
2. Stetson's situation: $2400 - 40x = 600$
3. Kit situation: $40x - 600 = 2400$

Would you like a detailed explanation of each equation or have any questions?

Here are some related questions to deepen your understanding:

1. How do you solve an equation like $2400 - 40x = 600$ to find $x$?
2. What is the process of translating word problems into equations?
3. Why is the equation $(600 + 40)x = 2400$ used for Leilah's flashcard situation?
4. How would the equation change if the kit's total mass was different?
5. What would happen if Stetson's rent increased or decreased?

Tip: When translating word problems into equations, focus on identifying quantities and their relationships. Look for keywords like "per," "each," "total," or "left," which help to set up the structure of the equation.