Atour group charges a flat price for a tour of up to 20 people. the cost per person varies inversely with the number of people. if five people pay 135 each, what must 15 people pay per person.

15 people must pay 45 unit currency each

Explanation:
Assume that the number of people is x and that the price per person is y.
We are given that the cost per person varies inversely with the number of people.
This means that as the number of people (x) increases, the cost per person (y) decreases and vice versa

This can be translated into the following equation:
y = k / x
where k is the constant of proportionality.

Now, we need to get k.
We are given that:
for number of people (x) = 5, the charge per person (y) is 135.
Substitute with this in the above equation to get k as follows:
y = k / x
135 = k / 5
k = 135 * 5 = 675

The equation now became:
y = 675 / x

Finally, we want to get the cost per person (y) when the number of people (x) is 15.
All we have to do is substitute in the above equation to get the y as follows:
y = 675 / x
y = 675 / 15
y = 45

This means that, for a group of 15 people, each one will pay 45 unit currency

Hope this helps :)