Question

6x2 - 2x - 3 + 5x - 7x2

Answer 1

Ok..well,not seeing what it asks, but i guess you want to simplify it.
The solution is simple, add the numbers that have the same variables. For example 6x squared plus -7x squared is -1x squared. 5x plus -2x is 3x. so it's:
3x-3-1x

Answer 2

Also, just for future reference, look at the expression closely, look at their variables and see if they're the same. Like x, that's a variable, even it's squared, its a variable. So if you see 2 x squared, they are the same. BUT, if you see x and x squared, they aren't the same
And also, be careful of the sign before the number and variable like -7x squared, you need to watch out for that, some people usually make that mistake and ignore it.