Give the step-by-step reasoning process and then the final answer. Susan had a sum of money. She spent 1/5 of it in September, 1/4 of it in October, and $120 in November. After spending these amounts of money, she still had $540 left. How much money did she have at first?
Let X be the amount Susan had originally. Susan spent 1 / 5 * X in September, 1 / 4 * X in October, and $120 in November. Susan has X - 1 / 5 * X - 1 / 4 * X - $120 = $540 left. Combining like terms, we get 11 / 20 * X - $120 = $540. Adding $120 to both sides, we get 11 / 20 * X = $660. Dividing both sides by 11 / 20 we get X = $1200.
The final answer: 1200.