How add a extra charge to apply to each user

Hi,

We want to configure a extra option for some tours, this extra would have to be applied to each user who books the tour.

By example, the tour costs 20 euros, and the extra option 5 euros.

So, if someone books for 5 persons with the extra option marked, the total cost would be 125 euros (100 normal price + 25 for the extra selected).

But we don´t know how configure the price/variations, or if this is possible.

What we want is update the total price for each person with the extra is selected becouse it is a extra to apply to each user.

How can we do this?

Thanks for your help.