Help: Combining a column reference with a number calculated in a cell

Hi,

I'm trying to find out how to combine a column with a number that I have calculated. For example, I have a formula which works out the length of the column which is:

=LOOKUP(2,1/(B:B<>""),ROW(B:B))

Which in this example outputs 1792 in cell I7

I now want to be able to plot into a line graph something like this C3:C (and the value of) I7

I've got a lot of graphs to make and so automating this with a macro would save me a lot of time but the issue is that the number of rows is always changing and I always want to start from C3

I hope this makes sense. I'd really appreciate it if anyone could help me with this