To make a cubic model you will need at least points. With these points you can find using basic algebra or with matrices.
What other information do you have?
Before you attempt substitution do you have a start year (or initial point) for the data?
Otherwise will mean the year and maybe not representative of what you are trying to model.
No, the data starts at 1950. Could I possibly translate the data so that 1950 is my start date?
So that would make d=554.8, right?
Then would I substitute that in the other equations, or should I use matrices?
Thank you so much =D
You were a huge help!