Describe a Situation with two quantities that have proportional Linear relationship

I went to a store to buy pencils.
The pencils cost 25 cents each.

1 pencil costs 25 cents.
2 pencils cost 50 cents.
3 pencils cost 75 cents.
10 pencils cost 250 cents ($2.50)

The relationship between the price of pencils and the number of pencils is linear.