Loretta picks apples for her grandfather to make apple cider. she brings him her cart with 42 apples. her grandfather smiles at her and say’s, you loretta. that is 40% of the apples that we need.”

One way of answering this question is to use division and multiplication and logic.
So you know that 42 is 40% of the total, so if you divide that by 4 you get 10.5, 10% of the total.
From there you can multiply it by 10 to get 105, 100%
She need to have a total of 105 apples