How would I solve this derivative and what does a=6 mean and how would I use it?

Use a graph of f or some other method to determine what, if any, value to assign to f(a) to make f continuous at x = a. HINT [See Example 2.] (If there is no such value, enter NONE.) f(x)= 174 x-12x + 36. X-6 ; a = 6