How to merge data from multiple columns into one column

[Thanh Binh]

I have a sheet that obtains the responses from a Google Form (Response Data.png).  The form requires each user to input 3 different purchases and their costs.  I would like for this data to be then merged so that, instead of appearing in multiple columns, it appears in one column but in the order that the data was entered (Desired result.png).  I have tried what I thought was the simplest solution (AttemptedSolution.png) but the pattern of cell references is not understood by Google Sheets and therefore can't be copied correctly.  I would love to hear of a solution?

Thankyou in advance.