Mrs. Green likes to fill the windowsills in her classroom with indoor plants like orchids and spider plants. To help them grow better, she sometimes adds fertilizer to her watering can. The amount of fertilizer she uses varies directly with the volume of water in the watering can.

Fertilizing indoor plants
volume of water (pints) 4 8 20 24
amount of fertilizer (teaspoons) 1/4 1/2 1 1/4 1 1/2
How much fertilizer does Mrs. Green use with 10 pints of water?