How do I make my form add up a total at the end?

Hi everyone! I am trying to make a custom wholesale order form for my site, where they fill out the form and then we send them an invoice, however I would like it to display the total at the bottom of the form before they submit it. Is there a way to do this? They just fill out the quantity of each product which I already have set up, the form is assigned a numeric value and thats multiplied by the quantity? 

For example:

Item 1: (customer enters 2) (x $20)

Item 2: (customer enters 4) (x $15)

Item 3: (customer enters 2) (x $10)

Total: $120

then they can submit the form and we do the invoicing from there. Is this possible?