You can put this solution on YOUR website! If you earn $2 a week and your parents match that, it means you get another $2. So in total, you get 2+2 = 4 dollars per week.
If x is the number of weeks and y is the total amount of money you have after x weeks, then you'll have dollars after x weeks. In this case, it only applies for 8 weeks, so x ranges from 1 to 8.
week 1: $4
week 2: $8
week 3: $12
week 4: $16
etc etc all the way up to week 8