2. the usual toll charge over the bridge is $1.50. if you purchase a special sticker for $10.50, the charge is only $0.80. at least how many trips over the bridge are needed before the sticker would cost less than the toll charge?

The trick is to figure out how much faster is starts costing at 1.50 a toll, compared to when you start by spending 10.50, but then spend less each time.

Think about how with the sticker you have spent 10.50, and then add the .80 for each new toll. At the same time, add 1.50 for each new toll without the sticker and keep track of the total. The place where they pass each other is where it starts costing less.

There are a few ways to solve this, including a table and an equation. Hope this helps you get started and let me know if you need more help.