Multiply the first equation by -2
-30-5x=-4x-6(5+4x)
First, you need to use the distributive property on the right to get -30-5x=-4x-30-24x
Then, you can add like terms to get -30-5x=-30-28x
Then, you can add 30 to both sides and add 5x to both sides to get 0=-23x
Finally, you divide both sides by -23 to get 0=x
The difference quotient or simply the derivative of a function is,
Here the derivative is,
So the difference quotient of your linear function is its slope namely 2.
Hope this helps.