Summing two column values and getting the difference with Laravel/SQL query

I want to sum two related model values seperatly, then get the difference of the two columns. Shop has productImages, product image has original size and optimized size. Need to sum original size, optimized size seperatly, then get the difference of them, which will be result of size saved.

 $shops = Shop::with(['productImages' => function ($q) {
        $q->???;
    }])->get();

I need to get the result in one query, how could I achieve this, that I could reach shops size saved value?

via Chebli Mohamed