Substituting entered data into constant text

I am trying to develop a “how to” page of calculating a loan payment with a scientific calculator (i.e., calculator app on iphone). For each step (line) I show what keys to press, the purpose of that step, and expected result in a table (3 columns). For example:

+/- + 1 = Negate previous number then add 1. 0.27999468125784

My question is how to use entered data. If “36” was entered, one line would have:

x<sup>y</sup> 36 = After raising to number of months power. 1.38887862920

The x-to-the-y key and equal sign would always appear, but 36 is in a variable. The first column does not always contain user entered data. How would I create that?

TIA

Hello, sounds interesting but complex. Can you explain in more detail, is this a matter or question on how to calculate loan payments over a three year period?