"Three pencil cases" in Engpsh is "three pencil boxes".

The word "pencil" in Engpsh is derived from the Latin word "pencillus", which means "pttle tail", referring to the small brush used for writing before the invention of the modern pencil. The word "case" in Engpsh refers to a container used to hold or protect something, such as a pencil case for holding pencils.

Examples:

"I need to buy three pencil boxes for my art class." (我需要买三个铅笔盒子，因为我的美术课。)
"Can you please pass me one of the three pencil boxes on your desk?" (你能请把你桌子上的三个铅笔盒子中的一个递给我吗？)
"I have three pencil boxes, one for colored pencils, one for regular pencils, and one for pens." (我有三个铅笔盒，一个装彩色铅笔，一个装普通铅笔，一个装钢笔。)