Use a piecewise linear model
A printer changes its per-batch rate after the first part of a print run
Let \(x\) represent print-run size (hundred-page batches), and let \(y\) represent printing charge (dollars). The model is valid from 0 to 8 hundred-page batches
The piecewise model is:
\[y = 23 + 2x,\quad 0 \le x < 4\]
\[y = 27 + x,\quad 4 \le x \le 8\]