How to set up calculations based on conditions?

I am also trying to find a way to value a count in a field being more than one. I have a poster counter that counts individual selections but have a selection option of a set of posters. i want this value to add 6 or 7 to the relevant final total of posters selected. i have added a value to each of the poster selections but this hasnt converted to the total number of posters.

I have cloned and tested your form on my end, I can see it works as expected since it counts the selected options you have specified on the "Number of posters picked" widget: 

It seems like you are already counting the number of selected options on your check box fields, I can also see you are already getting the total based on the selected options, as I can understand, you need to add an additional value in case the selected options is greater than an specific number. 

If so, you could do it with conditional logic, please check this guide in order to get more details about it: https://www.jotform.com/help/268-Conditional-Logic-Inserts-Text-Calculation-Into-A-Field 

I can also see you have some conditions where you are trying to calculate the discount value: 

The discount field is currently not calculating, this due to the fact that you are using the discount field in the calculation while it does not have a value, that's why you are currently getting 0 as result. 

I would recommend you to insert a fixed value instead of the discount field, if the multiplication has a 0 value then the result will be always 0. 

You may also provide us more details about the calculations you would like to perform, we  will be glad to help you to implement it on your form.