Sanjana brings 39 muffins to a bake sale. She only uses trays for groups of 10 muffins. Each plate holds only 1 muffin. How many trays could Sanjana use to display the muffins?

The correct answer is: 3

Sanjana has 39 muffins: 39 is 3 tens and 9 ones.
Sanjana puts 1 ten (10) muffins in one tray. She has 3 tens muffins.
Hence Sanjana uses 3 trays to display the muffins.