If this is just an expression, not an equation, and you have to simplify it, use order of operations.
So first, since there’s nothing to simplify in parentheses and no exponents, multiply by distributing -3/5 to 2/3m and 1. So the expression will be (I’m assuming the first 1 is not part of this)
2/5 m - 2/5m - 3/5
Now subtract from left to right. That gets rid of 2/5m and we’re left with -3/5.