Link a text box to a dropdown list selected value

I have a drop drown list with 5 names in an Adobe Acrobat PDF. Based on the person's name you select in the drop down list I would like the text box to auto populate with that person's phone number. For instance:

Drop Down List Field Name ('Name')

Jake

Bob

Maria

Phone Numbers Field Name ('Number') in order for simplicity Jake's number is 100 and so on.

100 //Jake//

200 //Bob//

300 //Maria//

My code is not working and I am close to figuring it out, do you know what the problem is?

var x=100;

var y=200;

var z=300;

if(this.getField('Name').value='Jake')

    this.getField('Number').value=x;