Can someone please explain how to solve this type of question?

Question

Determine the maximum and minimum value of the function f(x)=3x3^x - 1

Answer 1

y = 3x 3^x - 1
y' = 3*3^x + 3x(ln3)3^x
= 3*3^x * (1+x ln3)
So, y'=0 when x = -1/ln3

That is the only extremum. Now find whether y" is positive or negative there to determine which kind.