You would need to use javascript for this.
Something like this:
$(document).ready(function () {
$('#q102').on('blur','input', firstfield);
function firstfield() {
if($('#q102 input').val() != "")
$('#q106').val() = '';
$(document).ready(function () { <----- standard starting javacode
$('#q102').on('blur','input', firstfield); <----- If info in field #q102 has been changed.
function firstfield() { <----- start of function
if($('#q102 input').val() != "") <------ If field #q102 is not empty
$('#q106').val() = ''; <------ set field #q106 to blank
if you have more fields that needs to be cleared, you can add an additional $('#q106').val() = ''; and change the #qxxx value.
i.e.
$(document).ready(function () {
$('#q102').on('blur','input', firstfield);
function firstfield() {
if($('#q102 input').val() != "")
$('#q106').val() = '';
$('#q107').val() = '';
$('#q108').val() = '';