If Ms. Diaz saved up 300$ in 4 months, we know there are 8 more months left to save up for. To get to 1500, we need to start the equation with how much we have now (300) and how much time we have left (8m) where m stand for the amount per month.
300 + 8m = 1500
She would have to save a minimum of 150 a month to save up 1500$ in the next 8 months.
