3-5b=10+2bi'm not sure how to do this

3-5b=10+2b
We move all terms to the left:
3-5b-(10+2b)=0
We add all the numbers together, and all the variables
-5b-(2b+10)+3=0
We get rid of parentheses
-5b-2b-10+3=0
We add all the numbers together, and all the variables
-7b-7=0
We move all terms containing b to the left, all other terms to the right
-7b=7
b=7/-7
b=-1

Combine like terms 5b and 2b then you would end up with 3-7b=10 then subtract 3 from 10 and you would end up with -7b=7 

The scale factor of what ?