Define a Variable: Solution \& Interpretation: An online service charges nonmembers $\$ 4$ to rent each video game. If you pay a one-time membership fee of $\$ 21$, you can rent games for $\$ 2.50$ each. For what number of video game rentals is the cost the same for members and non-members? fine a Variable: Equation: Solution \& interpretation:

Step 1 ：Define a variable x to represent the number of video game rentals.

Step 2 ：Set up an equation to represent the cost for non-members and members. For non-members, the cost is \(4x\). For members, the cost is \(21 + 2.5x\).

Step 3 ：Set these two expressions equal to each other: \(4x = 21 + 2.5x\).

Step 4 ：Solve the equation for x. The solution is \(x = 14\).

Step 5 ：This means that the cost is the same for members and non-members when 14 video games are rented.

Step 6 ：Final Answer: The number of video game rentals for which the cost is the same for members and non-members is \(\boxed{14}\).