First, please explain what you want to do.
There are two problems that I can see.
1. You dont know how you can make the calculations in GUI.
2. You dont know how you can deal damage in GUI.
For 1,
When you are selecting a real or an integer, you will see this screen:
Under the "Function:" box, you can find the option "Arithmetic".
This option will give you a math function of 2 other reals/integers.
You can choose between +, -, * and /.
There are other options for maths under "Maths - ..." inside that same function box.
When you need 3 reals combined together, you have to make an Arithmetic inside one of the two reals given by the first Arithmetic.
In your case, you also want to use the level of an ability in your damage calculation.
This is an integer and your damage has to be a real.
So you will have to convert an integer to a real using the option "Convert Integer to Real" in the functions box.
There you can select "Level of ability for unit" to get the level.
In your case, you want to do:
( Base<1680> + ( Scaling<1680> * ( IntegerToReal( LevelOfAbility ) ) ) )
For 2,
Create a new action for "Unit - Damage target".
In that one, you can apply your damage to the target.