Sum of values

Hello,

I want to make a form on which people can request space for an advertisement banner.

Now I need a function which van make a sum of a value and put the outcome in a seperate field.

For example placing a top banner on my website will cost you 5 euro a week. I want the visitor to fill in the amounts of weeks they want their banner on my site.

So the form looks like :
***
How many weeks do you want your advert on our site:
Fill in amount of weeks (required) … (example 10)

Read only field displaying 50 euro.

***

And if that is possible what i am hoping for. Can i show that amount in the email sended to me and the visotor?

I tried to make a sort of example in english.. example

I’m sorry if this is asked earlier but I couldnt find an answer.
Thank you in advantage

jap

https://www.ads-software.com/plugins/contact-form-7/