2. A book with a green sticker costs $2 less than half the price of a
book with a yellow sticker

I need help with this one

For this case we can propose an equation that will allow us to find the price of one of the books knowing the price of the other.

x: Let the variable that represents the price of the book with a green sticker

y: Let the variable that represents the price of the book with a yellow sticker

According to the statement we have:

Finally, we can substitute the price of one of the books and clear the value of the other as the case may be.