By default, Soulver displays a total of all your lines in the bottom right hand corner.
In many cases, you can simply paste in a set of lines from the internet and get an instant total.
If the total is not helpful in your particular workflow, you can hide it by hovering over it and clicking
Press ⌘T or hover over an answer and click the make subtotal button (the middle button) to make a line a subtotal. A subtotal line will add up all lines above, up to the next subtotal