If / Then formula

I'm trying to write an If/then formula that says if the total number of items is equal to 1, then the shipping cost is 7.00. If the total number of items is more than 1, then the shipping cost is the total number items * .50 + 7.00.

This is my attempt at that formula that is not working.

If(Total_Number_of_Item)==1,7.00,Total_Number_of_Item)*.50+7.00)

Can I get some help with writing the correct formula?