Just multiply -3x by minus one.
For the second problem:
You could have just multiplied out instead.
I did two problems just now and both had positive answers, while I mistakenly got negative answers.
I thought it would equal 3x, since x - x = 0 and 0 - 3x = -3x
The other, While I got the opposite answer.
Can anyone explain why these answers aren't positive?