Camping Trip Cost Sharing Problem

A group of friends is planning to organize a weekend camping trip. The additional costs for food and supplies is shared equally among the attendees. Let N represent the number of friends joining the trip. If the total cost of food and supplies is $240, and an additional charge of $40 is incurred for renting camping gear, the formula for the cost per person can be expressed as:

$$C(N) =\frac{240 + 40}{N}$$

What is the minimum number of friends that must attend the trip so that the cost per person does not exceed $40?