Let us consider the case : a discount card which will cost you $160, and then $20 per movie.
For x number of movies, Your cost is,
[tex]160+20x[/tex]Taking the second case: $40 per movie. Foe x number of movies, your cost is,
[tex]40x[/tex]So, when the total cost is same,
[tex]\begin{gathered} 160+20x=40x \\ 160=40x-20x=20x \\ \frac{160}{20}=x \\ x=8 \end{gathered}[/tex]So after 8 movies, the total costs of the two options will be the same.