Applescript to change Page setup in PowerPoint for Mac

Very new to AppleScript. I'd like to change the Page Setup to "On-screen show (16:9)". Within PowerPoint it is under File>Page Setup>Size>Slides sized for : On-screen Show (16:9). I did find within AppleScript that the Slide Size is a Property of the Page Setup Class within the Microsoft PowerPoint Suite. It is also listed under the Application Class >Command Bar Class>Command Bar Control. The Page Setup inherits it's properties from Base Object.

I tried to manually record the process of opening a PPT file and choosing File>Page Setup>Size>On-screen show (16:9) but it only recorded the process to activate PPT and open the file.

I wrote this script:

tell application "Microsoft PowerPoint"

activate

open {file"MacBook Pro Hard Drive:Users:Patrick:Desktop:AppScript.pptx"}

set slide size to "on-screen show"

end

I get the error "Syntax Error : A property can't go after this identifier" and "slide size" is highlighted.

I'm stuck......Slide Size is a property of the Page Setup Class. How should I write this ?

Script Editor V. 2.7(176) and PowerPoint for Mac 2011