Using response to a question in a later question.

Hi,
I am new to qualtrics; so feeling a little lost. But here is the scenario I am facing.
I have to set up an experiment where participants are asked a quantitative prediction question (what is the weight of this person, for instance). Once they have made a predication, I show them the prediction of one other participant. This prediction that is shown to the participant can be close to or far away from their initial prediction (this is my manipulation). Hence, based on the experimental condition, I need to use the participants initial estimate and add/subtract a fixed number from it and show them the prediction. My question is how to use a participant's previous response in a later question/text.