Let T be total number of milligrams of vitamin C in our salad.
We have been given that there are s milligrams of vitamin C per milliliter of spinach, B mg per milliliter of berries, and D mg per milliliter of dressing.
Let us find how much mg of vitamin C our each ingredient of salad will have.
We have been given that a salad contains 300 milliliters of spinach, 200 ml of berries, and 42 ml of dressing.
To find total milligrams of vitamin C in our salad we will add milligrams of vitamin C in each of three ingredients of salad.
Therefore, our desired expression will be .