Create button “Add” to add a new row in sheets [duplicate]

Question

I'd like to know how to add a new row copying all formulas from previous row ..

What I'm looking for is as follows

 SR. NO     ITEM CODE       DESCRIPTION       UNIT COST
     1       5463345       (A V-LOOKUP)     (A V-LOOKUP)       [ADD BUTTON]

     2 

By pressing the Add button will create a new row with Sr. No 2 (automatic) and copy all the formulas from previous row with a new add button .

I know how to create a button(drawing) and attach script only thing is don't know what the script is to be :( There is also another submit button in this page which will take all these data into a newly created sheet (so far success) Entering the item code will thus add all the required values.