Jennifer bought a textbook with 2/7 of her money. She then bought a notebook with 3/5 of her remaining money and was left with $12. How much money did she start with.

X=amount of money at first

price of a textbook=2/7 x

her remaining money after she bought his textbook was: x - 2/7 x=5/7 x

price of the notebook: (3/5) (5/7 x) = 3/7x

her remaining money after she bought his notebook was $12

We can suggest this equation:

2/7 x + 3/7 x + 12=x

lowest common multiple=7

2x+3x+84=7x

7x-2x-3x=84

2x=84

x=84/2

x=42

Answer: the amount of money at first was $42.