Question10. A movie theater offers a reward program that charges a yearly membership fee and a discounted rate per movie ticket. The total cost for a reward program member to see 5 movies is $\$ 40$ and the total cost for 12 movies is $\$ 75$. Assume the relationship is linear. Write the equation of the function in the form $y=m x+b$, where $x$ represents the number of movies and $y$ represents the total cost.