Go back to Order of Operations if you are not sure what to do first with this question.

−5[−2(m − 3n) + 4n]

The square brackets [ ] work just the same as round brackets ( ). We could have used curly brackets { } here as well.

The first thing we do is expand out the round brackets inside.

−2(m − 3n) = −2m + 6n

The negative times negative in the middle gives positive 6n.

Now add the 4n in the square brackets:

[−2m + 6n + 4n] = [−2m + 10n]

Remembering the −5 out front, our problem has become:

−5[−2m + 10n] = 10m − 50n

Taking each term one at a time, what we did was:

−5 × −2m = 10m (Two negative numbers multiplied together give a positive); and

−5 × 10n = −50n (Negative times positive gives negative)

Go back to the section on Integers if you are not sure about multiplying with negative numbers.

So here's the answer:

−5[−2(m − 3n) + 4n] = 10m − 50n