D. 7.5 servings per batch
because there’s 22.5 servings per 3 batches, so to find how many servings there are per 1 batch just divide the servings by 3 to get 7.5.
Or you can cross multiply by setting up the equation 3 / 22.5 = 1 / ?, then multiply diagonally (22.5 x 1 and 3 x ?) and they should equal the same number so you get the equation 22.5 = 3x, divide both sides by 3, and 7.5 = x
Hope this helps.