You can do that with JavaScript but it's a little tricky if both questions are on the same page. When do you trigger the hide/show function? On every keystroke in the input or when the input is changed (which requires the respondent to click elsewhere on the page)?
Probably simpler would be a workaround like this - manual.limesurvey.org/wiki/Workarounds:_...ble_Text.29_question
Probably simpler would be a workaround like this - manual.limesurvey.org/wiki/Workarounds:_...ble_Text.29_question