Script to add a new row and copy the formula that is in each cell

Question

I am trying to work out a script so that when I press the + image on the attached screenshot it adds a new row and copies the formula that is in each cell. At the moment, I have the following script which adds a new row:-

function insertRowsAfter() {
  var ss = SpreadsheetApp.getActiveSpreadsheet()
  var s = ss.getActiveSheet()
  var cell = s.getActiveCell()
  var row = cell.getRow()
  
  var num = Browser.inputBox("Enter No. of rows:")
  s.insertRowsAfter(18,1)
}

I need to add to the script so that the formulas in cells B18, D18 & E18 are included.

These are the formulas in each cell:

Cell B18 - A script is used to reset this cell so that it reads "Select Extras". This script is as follows:-

function ClearCells() {
var sheet = SpreadsheetApp.getActive().getSheetByName('Calculator');
sheet.getRange('B7').setValue('Select Panel');
sheet.getRange('B8').setValue('Select Mounting Equipment');
sheet.getRange('B9').setValue('Select Inverter');
sheet.getRange('B10').setValue('Select Smart Meter');
sheet.getRange('B13').setValue('Select Extras');
sheet.getRange('B14').setValue('Select Extras');
sheet.getRange('B15').setValue('Select Extras');
sheet.getRange('E3').setValue('Select');
sheet.getRange('E4').setValue('Select');
sheet.getRange('E5').setValue('Select');
sheet.getRange('C8').setValue('=ROUNDUP(C7/6,0)');
sheet.getRange('C7').clearContent();
sheet.getRange('C9:C27').clearContent();

}

Cell D18 - The formula here is: =IFERROR(VLOOKUP(B18,Extras!A5:B24,2,FALSE),0)

Cell E18 - The formula here is: =+C18*D18

If someone can assist me that would be great.