Answer: -12w
Your expression is the same as 1w-4w-9w, because the first w has a coefficient of 1. Now, you can just subtract the variables from each other.
Doing this is pretty simple- you just do (1-4-9)*w. 1 minus 4 is -3, and -3 minus 9 is -12. So the answer is -12w.
So, all you're doing is subtracting the coefficients from each other!