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.

# Answer

1200
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
1200
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?
train