What was the question for this implicit rationale, and corresponding answer?
Since Michaela needs 20 oranges to eat to her full, and Cassandra eats twice as much to have her full, Cassandra needs 2 * 20 = 40 oranges to eat. They eat 20 + 40 = 60 oranges together to have their fill. If they picked 90 oranges today, after eating 60 together, 90 - 60 = 30 oranges would remain.
 The answer: 30
The question: To eat to when she gets full, Michaela needs 20 oranges. Cassandra needs twice as many oranges as Michaela to eat until she gets full. If they picked 90 oranges from the farm today, how many oranges would remain after they've both eaten until they were full?