Tesla sells internet connectivity for its cars for $100 per month by buying the bandwith from a third-party mobile company for $30 per month per customer and wrapping the service in its own Tesla-developed user interface for an additional cost of $5 per month for each customer. Tesla pays a total of $5,000 per month for one customer service person who answers questions about the service and trouble shoots. Answer the following questions regarding Tesla's connectivity service (ignore taxes).

What is the contribution margin customer derived for each month of connectivity per customer?

a) $35 per month

b) $30 per month

c) $100 per month

d) $65 per month

e) $40 per month