Question 74278
If you are subtracting, a major error can occur.  WATCH YOUR SIGNS!!!
{{{ (9x^2-3)-(7x^2+6x) }}}
In your problem you forgot the 'x' with the 6.
Distribute the negative
{{{ 9x^2 - 3 - 7x^2 - 6x }}}
{{{ 2x^2 - 6x - 3 }}}