Answer:
Let x = amount of videos viewed
Let y = the total cost of the streaming service
Plan 1 Equation:

Plan 2 Equation:

Explanation:
Here we are looking to define our variables, and then form equations using them. We can use the slope-intercept form equation >
, where m is the slope, or the amount per viewed. X is how many videos have been viewed, and b is the flat rate, or how much at the start of the month.
The 1st equation requires 7 dollars a month along with the video fee, but the second one doesn't have a fee, so we don't include b.
Using the formula for slope-intercept, we can plug 2.5 and 7 for plan 1, and 4 for plan 2.