How to make excel create a formula for a cell to equal a value

Please say more about this. What you're asking is unclear.

example
45 + 11 = 56
45 * 1.244 = 56
and so on

Okay, so I don't think you're asking how to do those formulas in Excel, are you?

=45+11
=45*1.244

Are you asking why those two formulas might not show the results are equal to each other?

The first renders the whole number 56, while the second one results in 55.98. If you want them to be exactly equal, you would use =ROUND(45*1.244,0) to get a result rounded to the nearest whole number, or 56.

Do you mean you want the cell to be highlighted if it's equal to a specific value? Like conditional formatting?