I have a business that i need to add percentages of the invoice to the total. I have two line items that i need to do this for, but when i add a subtotal it will add everything up above it; like it supposed to!

When i add the 2nd subtotal in it will not add the first subtotal. It will only add the item i needed the percentage that i needed the first subtotal for. How do i make the 2nd subtotal add to the first one?