I have this page for taking signatures, I had a weird idea of storing them on one variable sized pen input - image below:

the pen input is split by lines that are there essentially to just give guidance. It is one singular input.
What I want to do is take the number from the dropbox on the bottom left, and use that to multiply the height of the box - the pen input however is inside of a gallery.
My main question is, is this doable and how would I go about it?