Identifying a question within roster

I have a fixed item roster of 5 rows a1 a2 a3 a4 a5 and two columns
For each of the column,
a5 is actually (a1+a2+a3+a4)
Is it possible to automatically populate a5 with the sum once the values for a1-a4 are entered

Make a5 a variable whose value is the sum these 5 rows. Because variables’ values are hidden during the interview, you would need to do the following to make them visible: create a static text and pipe the variable value into the static text via the substitutions (e.g., The value of a5 is %a5%).