/sci/ - Science & Math

I'm probably retarded but I don't know where else to ask.
/dpt/ perhaps?
Either way.
I'm trying to write a formula that spreads the required amount to return to neutral over the next 7 entries.
So in this neutral is 1500, and the first 2 entries in total were 700 over.
So I want the next 7 entries to be 1400, but I can't wrap my fucking head around how to write this.
I currently just have

=1500-((SUM($H3:H$4)-COUNT($H3:H$4)*1500)/7)

But this calculates it every time, so it won't ever return to neutral.
Is this an excel question or is this a maths question?
Am I retarded?