As I said before, you can't put "-6" like this into an equation.
What you also need to do is put it into {}. You should go in baby steps (that is how you should work in programming anyway. If you write loads of code and it does not work you have to debug loads of code. If you go step by step and check if it works, then you know at which step the error was.
Does it give you the correct value of the sums of the first subquestion of those questions? Try it and test it if it works. If it works, continue with the next step. If it doesn't work we need to debug this first step.
Then go for the next step and see if including "-6" into the sum works. I actually don't know if this can be done in one step. I would try 2 options:
and
and see what happens.
What you also need to do is put it into {}. You should go in baby steps (that is how you should work in programming anyway. If you write loads of code and it does not work you have to debug loads of code. If you go step by step and check if it works, then you know at which step the error was.
Does it give you the correct value of the sums of the first subquestion of those questions? Try it and test it if it works. If it works, continue with the next step. If it doesn't work we need to debug this first step.
Then go for the next step and see if including "-6" into the sum works. I actually don't know if this can be done in one step. I would try 2 options:
and
and see what happens.
