Question 78635
I assume the question is just to simplify the expression.
Let me re-write it first, since all my keys work :-)

{{{(3a^2-2a+7)+(a^2-3a-4)}}}

To simplify this expression, you need to combine "like terms."
"Like terms" are those terms that have their variable raised to
the same exponent. For example, 3a^2 and a^2 are "like terms."

So, you can re-write this as:
{{{4a^2-5a+3}}}

If, like I said, the problem was jusst to simplify the expression,
then that is the answer.