1) Simplifying linear expression with rational number means, we are dealing with numbers which are in fraction form, and are proportional to other side.
For Example. - 7x/3 = 21/6
In this example, when we solve for x, it would be rational number & as expression is proportional, it fits best for your question!!
2) Factorization (finding factors) of linear expressions:
For example. - 20 + 40 = 2 * 10 + 4 * 10
Here, linear expression is solved into simpler forms
Hope this helps!