I don't even know if this is an nth partial sum of a geometric sequence problem but...

if someone wanted to save money to buy a used car and they saved $100 on the first day, then $75 on the second day, then $56.25 on the third day, how much will they have saved on the seventh day?

In 20 days, will they have enough to afford a used car that costs $500?

what would be the total amount they saved in that time?

thanks