The four lines
The same four lines as every page of the Trace Press workbook. Tall letters (b, d, h, capitals) reach the top line. Small letters (a, c, e) stop at the dashed midline. Every letter sits on the solid baseline, and tails (g, j, p, q, y) drop to the dotted line below it. The line size is the distance from the top line to the baseline: 1" for ages 4–5, down to 0.45" for older children.
How many lines fit on a page
Writing lines on each page, by page size and line size, without bleed:
The page count doesn't change these: KDP's wider inside margin for thicker books takes width, not height. Bleed costs one line in three places: 5" × 8" at 0.45" (8), and 7" × 10" and 8" × 10" at 0.75" (6). A 100-page 8.5" × 11" notebook at 0.45" lines has 1,200 lines to write on.
Want the letters as well?
Trace Press makes a full A–Z tracing workbook: for each letter, capital and lowercase, a model with numbered start dots and stroke-order arrows, rows of dotted letters to trace, and rows like these for writing it alone. It includes the cover. It's free to try; $19 once makes it ready to sell.