Final answer:
The revenue per day from the charter can be expressed using the function R(x) = (540 - 7x) * (20 + x), where x represents the number of passengers above 20. To find the revenue per day for specific numbers of passengers, substitute the values into the function.
Step-by-step explanation:
(a) To find the function R, we can start by calculating the base revenue, which is $540 per person per day when 20 people sign up for the cruise. Let x denote the number of passengers above 20. For each additional passenger, the fare is reduced by $7 per day. So, the reduction in fare per day due to additional passengers is 7x. Therefore, the function R(x) can be expressed as:
R(x) = (540 - 7x) * (20 + x)
(b) To find the revenue per day if 48 people sign up for the cruise, we can substitute x = 28 (48 - 20) into the function R(x) and calculate the value:
R(28) = (540 - 7*28) * (20 + 28)
(c) To find the revenue per day if 78 people sign up for the cruise, we can substitute x = 58 (78 - 20) into the function R(x) and calculate the value:
R(58) = (540 - 7*58) * (20 + 58)