YOU SAID:

my teacher does not know how to do my math. (She cannot help me)

INTO JAPANESE

私の先生は私の数学のやり方を知りません。 (彼女は私を助けることができません)

BACK INTO ENGLISH

My teacher doesn't know how to do my math. (she can't help me)

INTO JAPANESE

私の先生は私の数学のやり方を知りません。 （彼女は私を助けることができません）

BACK INTO ENGLISH

My teacher doesn't know how to do my math. (she can't help me)