Linking Checkboxes and Radio Buttons

Hello guys i need your help,

i have 5 Checkboxes. Everyone of them can be checked or unchecked by itself. If the 5th Checkbox is checked, a RadioButton with 2 options should be activated. If the 5th Checkbox gets unchecked the linked Radiobutton should be unchecked and deactivated, so that both options are blank.

So my first question is what to write in js and my second question is where to write it or which trigger i need to choose.

I've tried it now for houres and didnt come to a close, i hope u can help me.

Below u can find what i already tried. "Chechbox5" is obviously the name of the fifth Checkbox and "RB_1" the name of the Radio Button. My Acrobat DC Version is 2015.006.30452.

Thanks

First Try

var source = null;

source = this.getField("CheckBox5")

if (source.isBoxChecked() == false)

{

    this.getField("RB_1").value = false;

}

Second Try

if (this.getField("Checkbox5").value == false)

{

    this.getField("RB_1").value = false;

}

Third Try

if (this.getField("Checkbox5").value == false)

{

    this.getField("RB_1").value = "Off";

}

Fourth Try

if (this.getField("Checkbox5").value == false)

{

    this.resetForm("RB_1");

}