Hello there!
To find the slope of a line in the from y=mx+b, look at the number behind the x. This means that your answer is the coefficient of the x term gives the slope.
This is not the case for any function that isn't linear. If it's not linear, finding the slope requires one to take the derivative of the function.
This is also why this is a horrible question because you only got rid of the x+b part BECAUSE you took the derivative.
Well again, your answer is the x-term. I hope this helps!
Best wishes :)