Answer:
For Company A, the relationship between months of service and total cost is proportional because there's a fixed monthly fee of $39.99 with no installation fee. The total cost increases linearly with the number of months subscribed.
For Company B, the relationship is not strictly proportional. While the monthly cost is $34.99, there's an additional fixed cost of $50 for installation, which is a one-time fee. The presence of the installation fee makes the relationship between months of service and total cost nonlinear, as the initial cost is higher but doesn't increase with each additional month of service.
In summary, Company A has a proportional relationship, while Company B does not due to the presence of the installation fee.