Question 164278
How's this... change all of the operations to addition. 
Negative numbers get parentheses around them.
Then sort and combine.
Maybe that'll work better. 
{{{3a-5-2b+3a+7b-2=3a+(-5)+(-2b)+3a+7b+(-2)}}}
{{{3a-5-2b+3a+7b-2=3a+3a+(-2b)+7b+(-5)+(-2)}}}
{{{3a-5-2b+3a+7b-2=a(3+3)+b(7-2)+(-5-2)}}}
{{{3a-5-2b+3a+7b-2=6a+5b+(-7)}}}
{{{3a-5-2b+3a+7b-2=6a+5b-7}}}