Answer:
If Ali has $9 and spends $2 each week buying chips. This means that the equation is: y = 9 - 2x. This is because the equation is calling for the amount of money Ali has left, which means that you have to subtract 2 times the amount of weeks passed from 9.
Week 1 ---- y = $7
Week 2 ---- y = $5
Week 3 ---- y = $3
You can also notice that each week the amount of money Ali has left decreases by 2.