Final answer:
The slope of the graph representing the cost a customer will pay for cable service with movie channels ordered is 12. This indicates a $12 increase in cost per additional movie channel.
Step-by-step explanation:
The function that represents the cost a customer will pay for cable service, given the number of movie channels ordered, is y = 12x + 50. To find the slope of this linear equation, we look at the coefficient of the x term. In this equation, the slope is the number that is multiplied by the variable x, which is 12. Therefore, the slope of the graph of this situation is 12. This means for each additional movie channel ordered, the cost will increase by $12.