Question: Provide a step by step solution for the following math problem: Mulan has $40. Her father gave her $100. She buys two pairs of jeans at $30 each and a bag for $20. How much money does Mulan have left?
Answer: 
Mulan has a total of $40 + $100 = $140.
Two pairs of jeans cost 2 x $30 = $60.
Thus, Mulan spends a total of $60 + $20 = $80.
Therefore, Mulan has $140 - $80 = $60 left.