<span>associative property of addition and answer is
</span><span>(u + 7) + 13 = u + (7 + 13)</span>
Think of it as -5+1i/2i, since 1i=i. From there, the i's could cancel out since dividing a number by itself would just equal 1. It would then be -5+1/2 which would be simplified to -4 1/2. No need to worry about those i's at all!
The GCF of the three terms (9a, -18b and 21c) is 3
Rewrite each of the terms so 3 is a factor
9a = 3*3a
-18b = -3*6b
21c = 3*7c
So we can say...
9a - 18b + 21c = 3*3a - 3*6b + 3*7c
9a - 18b + 21c = 3(3a - 6b + 7c)
Answer: 3(3a - 6b + 7c)
If you distribute outer 3 to each of the inner terms and multiply, you'll get the original expression again.
