Question 68696
What you're doing wrong is that you have to add and subtract like terms, subtracting 10 would not be a possible way. 

7x+3(2x+5)=10x+17
7x+6x+15=10x+17
13x+15=10x+17
-10x  -10x
3x+15=17
  -15-15
3x=2
/3/3
x=2/3