Two point three multiplied by m equals point four six.
That is the simple way.
But if you want to be more accurate, then you write it like this:
Two one point 3 tenths multiplied by variable m is zero point four tenths six hundredths.
These type of questions have almost nothing to do with math and don't teach students much but schools still insist on teaching it. There is a specific word for that: Unnecessary.