Number + 级 + Noun
级 (jí) is a classifier used for levels, grades, stages, or ranks. It appears when counting levels of a structure, stages of a rocket, grades in school, or ranks in a hierarchy.
这是一枚三级火箭。
Zhè shì yī méi sānjí huǒjiàn.
This is a three-stage rocket.
他现在读五年级了。
Tā xiànzài dú wǔ niánjí le.
He is now in fifth grade.
这场台风达到了十二级风力。
Zhè chǎng táifēng dádào le shí'èr jí fēnglì.
This typhoon reached force twelve wind strength.