The total cost for a 6-month plan for n lines is represented by the equation:
Cost = 660n + 100
This equation is in the slope intercept form. The coefficient of n represents the slope here.
In the given scenario the slope can be interpreted as the total variable cost for one line for a period of 6 months.
The variable costs are associated with a line are:
1) Unlimited data cost ($40 per month). So for 6 months this cost will be $240
2) Unlimited Call cost ($10 per month). So for 6 months this cost will be $60
3) Unlimited Text Message Cost ($10 per month). For 6 months this cost will be $60.
4) Cost of Phone ($300 per line)
Adding these costs up we get: 240 + 60 + 60 + 300 = $660
Thus, 660 represents the total cost per line for unlimited data, calls, text message and one phone for 6 months. Therefore, option A gives the correct answer.
