The above post is a naive implementation and it uses 2 TextBox objects. (TextBox1 and TextBox2) If you have 20 TextBoxes, having TextBox1, TextBox2 up to TextBox20 would work but it is ugly. You could go naive and create them like TextBox_Line3_Column1, Textbox_Line3_Column2 and Text_Line3. This works... but if you have to create 100 of lines, creating 100 lines manually would be hellish work.
If your requirement is just that or if it is unlikely to change later, you can just go with the paragraph above.
A more practical approach to iteration would be to have just 1 TextBox object, create many instances of them (copy and paste them) and refer to them using for loop and variables. The same goes with the Text object.
So instead, for the 7 lines, what I would do is to create a variable for the textbox and text object. Let's call it "LineNumber". Once you arrange those TextBoxes and Texts on your layout to be in the correct order, you set LineNumber for each TextBox and Text instance accordingly to the line they are on. For example, line 1 instances have LineNumber set as 1, etc. For the textbox instances, you will also need another variable called "column". For the Textbox instances on column 1, give this value of 1. Do the same for Textbox instances on column 2 but give them value of 2.
In the event sheet, you can do something like this:
global variable sum = 0
for i = 1 to 7,
set sum = 0
TextBox of variable Column 1 and LineNumber i: add int(TextBox.text) to sum.
TextBox of variable Column 2 and LineNumber i: add int(TextBox.text) to sum.
Text of LineNumber i : set text to global variable sum.