i have no idea what to do.

If the above is factual, then more assistance is required than likely can be provided online, and perhaps better course placement should be considered.

In hopes that the above constitutes hyperbole:

Mr. Scrooge started out with $300 more than Mr. Marely. After 100 days of hoarding, Mr. Scrooge had less than Mr. Marley had after just 70 days. Mr. Marely had been saving $10.00 per day. What is the largest amount per day that Mr. Scrooge might have been saving?

For simplicity's sake, one may start with three hundred and zero, since this clearly represents "three hundred more". How much does Marley have after the seventy days? (Multiply.)

Since Scrooge has no more than this amount after a hundred days, how much, at most, could Scrooge have added over the course of the hundred days? (Subtract.) Then how much could he have been saving each day, at most (as an average)? (Divide.)