如何从特定行PHP的sum（columns）函数中获取值

I'm trying to pull values from two columns based from an id. I have the following data in MySQL:

id | Rental | Rentals_Out
 1     11         11

I want to add both of those two columns in id 1. I've tried searching here and Google, but I haven't quite found what I'm looking for.

Below is the code I'm using

$sum_column = DB::select("SELECT SUM(Rental + Rentals_Out) as total_gowns FROM tbl_products WHERE id = '1'");

Or I don't mind using Eloquent but how do I enter multiple columns under pluck function? It seems to only work for one column, and I don't want to duplicate the code.

$sum_column = UCPost::where('id', 1)->pluck('Rental')->sum();

The code works under the raw SQL statement, but the output comes out as the following:

[{"total_gowns ":"22"}]

How do I get just the value i.e. 22?

You can try this:

DB::table('tbl_products')
   ->select(DB::raw('Rental + Rentals_Out as total_gowns'))
   ->where('id', 1)
   ->first()->total_gowns;