In march, a customer spent $8.55 at an office-supply store for some 12-packs of pens. at that time, the store was selling packages of one dozen pens for $1.35. any customer who bought more than 4 packages, received a discount of $0.30 on the price of each package in excess of 4 packages. in september, the same customer went back to the store to buy the same number of pens. by then, the price per 12-pack of pens had been raised to $1.50 each, with the same discount for more than 4 packages. how much more did the customer have to pay in september than in march?

We can start by making an equation from the information given on the month of March to find how many packs he bought.
This equation shows that for the first 4 packs he bought, he payed $1.35. Then, consequently, for each pack after that, he payed $0.30 less, and we don't know how many more he bought, so we set it up as shown. Finally, we set it all equal to $8.55 since that's how much he payed that month. We get that x=3, meaning that he bought a total of 7 packs of pens that month.
Knowing this, we can now make an equation for the month of September.
This time, we know the entire left side, that he paid $1.50 for the first 4 packs and $0.30 less for the last 3. We get x=$9.60
Knowing this, we can subtract the amount he paid in September by the amount he paid in March to get the answer... $9.60-$8.55=$1.05

I hope this helped!

The answer simplified would be. -6300x