$59 is the fixed cost of the phone and that will never change. This means it won't have a variable attached and will simply be added on to the cost
$39 is how much Jonathans will pay per month. This will change based on how many months pass. This will have the variable attached.
This means the formula is:
59 + 39m
Let me know if this made sense!
~Just a girl in love with Shawn Mendes