Question 2951
Okay, this is actually pretty simple.  Negative minus a negative is like adding the two numbers and then keeping them negative.  I know it sounds confusing, but I'll give you an example.  -3x-10x=?  For this, all you do is add the two numbers (3 and 10) and keep it negative.  Thus, -13.  Now, as long as the variables are the same throughout the entire equation, you just carry them through.  Back to my example, -3x-10x would equal -13x.  You see?  I'll let you solve your problem on your own, but if you're still having trouble, I'll explain further.  (HINT: Even if there's two variables, in your case a and x, just carry them both through!)