If/Else Statement from text to numbers in PDF Form

I would recommend that you learn how JavaScript works. It's not overly complex, and you can probably learn a lot about it in just an afternoon. A while ago I wrote a blog post about how to learn to program in JavaScript for Acrobat: Learning to Program JavaScript for Adobe Acrobat - KHKonsulting LLC

In general, an if else statement looks like this:

if (somethingIsTrue) {
  // .... if block
}
else {
  // .... else block
}

If "somethingIsTrue" is true, then the "if block" gets executed, otherwise the "else block".

So, in your example, the user picks the "STATE", and when STATE is set to "FL", you want FL_CALC to be 145, and otherwise you want FL_CALC to be set to 450:

if (this.getField("STATE").value == "FL") {
  this.getField("FL_CALC").value = 145;
}
else {
  this.getField("FL_CALC").value = 450;
}

This does not contain any error checking (e.g. what happens if the field "STATE" or "FL_CALC" does not exist?), so you may want to look into some exception handling.

The code as I've described it will work from e.g. a global calculation script. If you want to do a calculation script, you will need to set the return value for the event handler: You want to calculate FL_CALC based on the "STATE" field, so you will need to create a custom caulcation script for the field FL_CALC. There are more elegant ways to do this, but to keep it easy to understand, I would recommend you use something like  this:

if (this.getField("STATE").value == "FL") {
   event.value = 145;
}
else {
  event.value = 450;
}